Katz's Corner Episode 24: Pass Labs HPA-1 Headphone Amplifier

Fig. 1: Pass HPA-1 amplifier, front panel

Nelson Pass's Lab has produced an impeccable headphone amplifier with more than enough power, that's quiet, solid, and very clean. Several other reviewers have reflected on this excellent amplifier, but I want to weigh in with my unique sonic perspective and also measurements of its performance.

PassLabs_HPA1_Photo_RearPanel

Fig 2: Pass HPA-1 amplifier, rear panel

The Pass's sculpted front panel is very pretty and makes a distinctive show piece; there's no need to hide this baby. The rest of the case consists of rectangular brushed aluminum panels. Its large, weighted volume control is unique in my experience—rotational feel is more solid than any other rotary control I've ever used. It's also very precise, as I measured nearly perfect channel matching, zero error (level difference) at full gain, 0.06dB error at 3 o'clock and 0.25dB error at 12 o'clock. Jam Somasundram, its designer, has made a very wise decision, to set the voltage gain to the absolute minimum to be compatible with any current headphone and DAC source. It's specified as only 6dB though I measured 7.6dB gain into 20 Ohms at 1kHz. Even with the volume control all the way to the top, there is no noise to be heard with the most sensitive headphones.

He has implemented an unbalanced circuit, with two selectable stereo RCA inputs and a locking 1/4" TRS jack, yet it delivers plenty of power, demonstrating that it is not necessary to have a balanced output to produce superior performance. An unbalanced amp needs a higher voltage power supply than a balanced amp with the same specification—however, the tradeoff is that fully-balanced requires double the components and an expensive, high precision 4-gang volume control. Balanced is strictly a designer's choice, not demonstrably superior (or inferior) to unbalanced—if the designers optimize the characteristics of each design. Ironically, most times Nelson Pass has advocated a fully-symmetrical approach in his products, but not in this headphone amplifier, which has a clean, minimalist design and few active components to pass the signal through.

Yes, balanced inputs may improve hum performance when very long connections are used, but that is not the case in most consumer's homes. Balanced outputs for headphones are absolutely not necessary, and even the use of the term is questionable—I prefer to say "push-pull" because headphones are floating, they do not have a ground reference. The amplifier also has line level outputs, available at the press of the "preamp" switch. The line-level preamplifier comes direct from the headphone circuit with the addition of a premium coupling capacitor. I did not listen to the preamp output but I did test its functionality. Pass's technical support engineer Kent English points out "One of the goals was to enable 'not yet audiophiles', allowing them to hear their own music better than they have heard it before....for the first time. In other words build something that appeals to the music lover first, number chasers second."

Jam, who is a very enthusiastic engineer, gave me some insight on the design: The HPA-1 was designed as a small power amp, requiring an oversized power transformer and a +/-24 Volt DC supply, while most headphone amps suffice with only +/- 15 volts. The low feedback, wide bandwidth amp has J-FET inputs and a direct-coupled MOSFET output stage, fully biased in Class A throughout. But unlike a loudspeaker amp a headphone amp has to meet a huge bunch of conflicting requirements. It has to drive a wide range of loads, from very sensitive headphones with as low as 15 Ohm impedance that require high current, to insensitive headphones with impedance as high as 600 Ohms that require high voltage drive. So after a certain point design choices become subjective, deciding the least compromise in each area to ensure low noise, low distortion, wide bandwidth and good sound.

For example, there is a balancing act between negative feedback and open loop gain as too much feedback results in a shallow midrange. There are no integrated circuits in the signal path. The power supply regulator is discrete, which Jam says sounds better than an integrated circuit. It took a full year to perfect the design, which included choice of components by listening. Eliminating unnecessary components was a conscious part of the design, and with its optimized gain and imperceptible noise, Pass has avoided the need for complex gain-set switches, that can introduce noise or distortion if not set properly.

Measurements

I made some basic measurements to confirm performance. Voltage gain (unloaded) to either the preamp or the headphone output was 8.25/8.28dB at 1kHz. Loaded by 20 Ohms, the output dropped by 0.62/0.54dB, indicating an output impedance of 1.45 Ohms (left channel) at 1kHz, close to its specification of "less than 2 Ohms". This moderate output impedance indicates that high negative feedback was not a design goal, so to obtain good linearity the designer had to begin with a very linear open-loop circuit.

With a 1kHz tone, 0dBu output into 110 Ohms (5.5mW) produces nearly all 2nd harmonic, at a level of -90/-90dBu, or 0.003% THD. We can see a trace of 3rd and 4th harmonic peeking above the noise floor in the left channel only, but at insignificant level. The rest is noise and hum (See Fig. 3). Keep in mind that second harmonic is the most innocuous and "invisible" harmonic inasmuch as it is exactly one octave above the fundamental. Besides, a level as significant as 0dBu would yield a ridiculously loud 101.72dB SPL in the Audeze LCD-4 headphones (according to manufacturer's specification). The very low second harmonic is at an inaudible 11.72dB SPL! The absence of other harmonics is a testament to the very linear design and promise of good sonics.

There are also visible hum-related products near the noise floor, at a higher level than I've seen in some other headphone amplifiers. Nevertheless, this hum is inaudible with any headphone I own. The noise floor measured -95.63/-95.77dBu unweighted, 10-20kHz, so it is also inaudible. I measured an acceptable crosstalk figure (110 Ohm load) of -70dB (in either direction) throughout the majority of the spectrum, rising to -55 at 20kHz. An IM test, 19/20kHz at a total of 0dBu into 110 Ohms produced a 1kHz difference tone at a very low-105dBu and supersonic sums circa 40kHz at -75dBu, which represents very good performance (fig 4). The rise in noise floor above 40kHz is due to my Prism interface's noise-shaped converter.

For frequency response, I can measure up to about 80kHz, and within that bandwidth, I measured the Pass's response (unloaded) as ruler flat from 10 Hz (where I began measuring) and slowly rolling off to -2.25/-2.5 at 80kHz at 0dBu output.

PassLabs_HPA1_Graph_Fig3

Fig. 3: Pass HPA-1 THD at 1kHz and noise

PassLabs_HPA1_Graph_Fig4

Fig 4: Pass HPA-1 IM distortion

While attempting to measure maximum power output I ran into the first "limitation" of the HPA-1's low gain: I could not drive the amplifier into clipping with the Prism Callia's unbalanced outputs, whose maximum level at full scale is 2V RMS (+8.23dBu), the same maximum output level as a consumer CD player. The reason I put the word "limitation" in quotes is that the Callia's unbalanced outputs at full scale can drive the HPA-1 to a very healthy 15.96/15.99dBu (1.18 watts) into 20 Ohms at 1kHz, yielding 0.1% THD and which would produce a deafening 127.8dB SPL at full scale even with the insensitive Audeze LCD-4. Not an advisable condition, so the Pass's low gain is not a limitation at all. If you insist on driving your eardrums into submission you'll need a DAC or preamp with a higher level output. You could also get 6dB more level with a balanced to unbalanced adapter. Not advised!

Nevertheless, I persisted. I switched to an interface with higher output level, the Prism Lyra, so finally I can confirm that the Pass clips, with 1.07/0.7% THD at 1kHz, +21.28/+21.30dBu (4 watts) into 20 Ohms, 1/2 a watt higher than the specification. For the record, that is equivalent to an even more deafening 133dB SPL (LCD-4) which would certainly damage headphones as well as ears in continuous testing. This is a measure of what the amplifier can deliver on peaks, so if we subtract a nominal 20dB, it would satisfy some mythical listener with mezzo-forte passages of 113dB! Fogedabodit.

The Listening
I warmed up the unit for several days. The sound definitely improves throughout the first day, and I swear even after the seventh day of continuous power it keeps on sounding better. Pass advocates leaving the power on 24/7. I decided to pit the sound of the HPA-1 against the Mjolnir Pure Bipolar as a reference that I'm familiar with. I matched the gain of the Mjolnir (balanced) and the Pass (unbalanced) within 0.1dB at 1kHz into a 110 Ohm load. The Pass volume control was set to full level and the Mjolnir ended up at about 3 o'clock. I built a high quality TRS male to XLR 4 pin female adapter so I could quickly exchange balanced headphones between the two amps.

I used JRiver Media Center on PC to play high resolution files into the Prism Callia DAC via AES/EBU from my Lynx interface. JRiver fed Acourate Convolver via Acourate ASIO's 64-bit connection so that I could insert my custom headphone EQ filters if I wished, but I listened with no EQ (flat) to all my tracks. With the Pass driven by the Callia's unbalanced output, I was able to produce a "loud" presentation of a well-recorded popular music piece at -11dB digital attenuation. Acourate Convolver dithers all its outputs, so there's nothing to fear from its digital attenuation. This leaves up to 11dB available gain, enough to play the softest, widest range classical music piece in my collection. By contrast, the Mjolnir had additional available analog gain, conceivably to play even softer music, but I have never seen any recording that would require it, so I am convinced that the Pass has adequate voltage gain to handle any music you might decide to feed it.

Lindsey Webster "Back To Your Heart"

This is one of my own masters, at 2496. It's a full-bodied, full range smooth jazz recording. With the Pass, the sound is very attractive, punchy and fat. The sound is subtly on the warm side: Lindsey's voice sounds warm and intimate. The cymbals are round, clear, yet extended. The ambience seems reasonably wide; I don't notice any loss of separation. Bass is solid and deep.

Switching to the Mjolnir, the sound is also clean, pure, and extended from bottom to top. The recording's ambience stretches pleasantly, it seems a bit more outside the cans than it was with the Pass. Vocal is perfectly centered within my head. All the clarity is there and it's driving the transients effortlessly. I'm quite surprised that the Mjolnir seems a tiny bit brighter than the Pass on this material since I expected it to sound warmer based on previous experience. Bass is big and beautiful. The snare pops. Cymbals are pure and tight. I don't feel we're missing any high end, even though I'm not using the headphone EQ that I'm accustomed to using with the LCD-4s and the Mjolnir.

Switching back to the Pass, I notice the sound level seems to have dropped just a hair. Aha, that's a clue to the sonic difference: I wager that the Pass sounds a hair softer (even though the levels were matched) because it is much cleaner, has far less harmonic distortion than the Mjolnir. This gives the Mjolnir an unfair loudness advantage. I don't think it will ever be fair to compare these two amps at matched 1kHz levels so it's perfectly possible that the sonic differences amount to the harmonic distortion contributing to a perceived loudness difference.

Either way, the sound of the Pass is extremely satisfying, warm, natural and beautiful, just not as bright circa 8-10kHz as the Mjolnir with this particular recording, but we're talking about the tiniest hair, so small that even an expert could not decide which presentation is more "right". There is no "right" when two amplifiers are both this good. And frankly, I could not pass a blind test to determine which amp is playing, as there is more similarity than difference when the two amps are matched at 1kHz.

San Francisco Symphony, West Side Story

For this gorgeous 24/96 recording from Blue Coast Records, I had to raise the digital gain by 6dB—attenuation is now at -5dB. On this recording, which I know to be bright-sounding on its peaks, the Mjolnir is a bit more forgiving as it saturates at higher levels and gets warmer via the additional 2nd and 3rd harmonic, while the Pass remains linear. So when the Jets chorus sings loudly, the vocals sound sweeter and more palatable on the Mjolnir than the Pass. But for the vast majority of this recording, except for the fortissimo passages, the Pass sounds beautiful, warm and pure.

It's critical to note that when I play this recording on my speakers, I EQ the high end down or it would sound bright and a bit harsh. So when playing it flat through the Pass I hear the same issues as on my speakers and amp. It's clear that the Pass amp is subtly on the warm side of accurate, and the Mjolnir on the euphonic side, at least on the loud passages. A bit of program EQ would fix the presentation of this recording on the Pass. Recordings differ and some of them need EQ. Live with that!

Janice Ian, Walking on Sacred Ground

This is from the album "Breaking Silence", transferred from the 16/44 CD. I began with my headphones on the Pass amp. This excellent recording, mastered by Doug Sax, brings goose bumps! Doug's great tube transfer chain really makes this recording sound beautiful, sweet and perfectly reproduced on the Pass. The highs and transients in this recording are still punchy and clear without getting fatiguing. This segues into Janis' "Ride Me Like a Wave", which also does not disappoint. This is a very pleasant listening experience. I do not switch the Mjolnir to compare.

"Do You Remember" by Jill Scott.
16/44 from the album "All or Nothing". This Neo Soul album's bass, in tandem with bass drum, goes down very deep. Her voice sounds warm and full on the Pass. The transients really move, and there's effortless power to spare. This a reference recording for the soul fanatic where the touch of hip-hop feel provides the "neo". I do not switch to the Mjolnir.

"Erienda", by Kenny Rankin
From the album "Because of You", direct from the 16/44 CD that I was the recording engineer for. I recorded this song with minimalist miking, primarily a Blumlein pair, in RCA's Studio A, New York City for Chesky Records with a tube chain and custom A to D Converter. Kenny's voice is just as I remember it, filling the hall so nicely. Highly recommended, if I may say so myself. The tone of all the instruments is just right on the Pass. It's pure pleasure. The ambience of Studio A is reproduced and extended well outside the phones. I do not switch to the Mjolnir.

"Speechless", by Laurie Anderson
This is from the CD "Bright Red". Recorded by the great Kevin Killen, mastered by Bob Ludwig, this a mesmerizing and perfect reference for audiophile fans of rock and performance art. Pick it up right away if you are a Laurie Anderson fan. Pick it up even if you don't know who Laurie Anderson is. The drums are among the best rock drums on any recording ever made, ever! The dynamics are impressive and the Pass does it perfect justice, extending the ambience well beyond the sides of my head. Bass drum goes down to the center of the earth, or at least my head. Mesmerizing. Did I already tell you that? I do not switch to the Mjolnir.

FB Pocket Orchestra, "I Lost My Girl from Memphis"
This swing combo is from my 2496 master of the album "Guerilla Jazz". The Pass reproduces the instrumental and percussion transients particularly well, making me rock involuntarily with the rhythm.

My impression is that the Pass is an impressive, impacting and musical headphone amplifier with absolutely no defects. It's musical, slightly on the warm side, yet extremely true to the source.

Matt and David Take a Listen
Let's check the perspective of a couple of young audio ears: my two assistants, Matt Davis and David Corson, with different tastes in music, so let's see how their favorites play on this amp. (I did suggest some of the tracks). Initially they listened without any headphone EQ. Again, amplifier levels matched within 0.1dB at 1kHz into a 110 Ohm load.

Vienna Philharmonic, Mahler Third, 2488 from HD Tracks
Matt - On this piece I can't hear any appreciable difference between the Mjolnir and the Pass.

David - The Pass is very similar in tone to the Mjolnir. Though it's really close, the Mjolnir has more impact and microdynamics than the Pass. But the tonality is too close to call.

Lindsey Webster, "Next to Me", 2496 Master
Matt - Pass: Dynamic presentation far surpasses the Mjolnir's. In the Mjolnir, the kick drum is more restrained. The vocal doesn't jump forward as much on her peaks. I'm not hearing the 3D quality: This may be because the Mjolnir's slightly warmer than the Pass as a lot of ambience is contained in the high end.

David - The Mjolnir seems to have a boost in the lows below about 100 and perhaps a bit more presence and microdynamics throughout the whole range.

FB Pocket Orchestra "I Lost My Girl from Memphis", 2496 Master
Matt - The Mjolnir has a harshness and a veiled quality compared to the Pass. The Pass is not brighter. The 6k sizzle in the tambourine favors the Pass over the Mjolnir. The Pass seems sweeter in the highs.

David - The Pass seemed warmer on this one, but did not have as much bottom. Makes me think the Mjolnir has a bit of a smile curve. [BK note: I think the apparent multi-personality of the Mjolnir is because of the sonic unpredictability of 2nd and 3rd harmonic distortion. Sometimes it can sound warmer, sometimes a bit brighter, sometimes more dynamic, sometimes less, depending on the content and the listener's orientation.]

Deepest Crystal Black, "And Where Now", hard rock, by IceCocoon, 2496 Master
Matt - The Mjolnir: This is a thick, closed in mix. The sound is flabby. In contrast, the Pass is leaner, translates better. The Mjolnir is muddy, the Pass is clearer. They both express the deep sub range approximately well, but the sonic differences in the low mids can prejudice the impression of the deep bass.

David - The Mjolnir seems to bring out the bass more as well as the vocals seem clearer, more presence.

Miles Davis "So What" from Kind of Blue, DSD upsampled in JRiver to 176.4
Matt - The distinctions are very subtle in this particular track. The two amps are very close. These two amps are more matched than not.

David - Seems similar to my previous reactions.

Ray Charles: "Here We Go Again", 2496 from "Genius Loves Company" Anniversary Edition
Matt Pass: Does not feel brighter. All signs would point to that since it has a clearer sonic signature. But it feels natural, kind of makes the Mjolnir feel like a murky amp. The Pass has more dimension.

David - Similar to my previous reactions.

Fahrenheit by Telefon Tel Aviv on Tidal – electronic music, aka "IDM" (intelligent dance music)
Matt - Even on something this extreme the Pass has a depth of field that I miss in the Mjolnir. But if I heard the Mjolnir on its own it would stand out well. This is not a glaring issue, a matter of (my) taste.

David - It feels like the Pass is a bit warmer here. But the bass is apparently emphasized in the Mjolnir.

Bruno Mars, 2496 MQA on Tidal "That's What I Like" from "24k Magic"
Matt - This is a nice, well-balanced master by Tom Coyne, a warm but incredibly punchy track, a great reference. My idea of a perfect EQ balance. There is an additional warmth in the Mjolnir that I don't hear in my studio. The Pass is a more present amplifier, and I hear the sound as I do on my system. This comes down to a matter of taste, which sound you prefer and why.

[Bob: Now I throw a monkey wrench in the works, my LCD-4 EQ] With the EQ, now this song feels thin with the Pass and the Mjolnir sounds more like the Pass did without EQ! It could be that the Pass is imparting a subjective Air band boost. The Mjolnir is more "tubey". The triode-like saturation in the Mjolnir can be desirable.

I really like the cleanliness of the Pass. The EQ helps the Mjolnir but I still can't shake the feeling that there's an alteration going on in the midrange. I can see some people seeking that character but in this range I seek neutrality. Most people would prefer the Mjolnir when Bob's headphone EQ is applied.

David - Similar reactions, except now the Pass seems warmer from 60 through 500. But the really thumpy bass is greater on the Mjolnir.

Summary
Matt enthusiastically preferred the Pass to the Mjolnir. Matt and David sometimes differed in their reactions, a matter of taste, but keep in mind the Mjolnir was designed to emulate a classic triode circuit, which saturates a bit as things get loud. Single tone tests on the Mjolnir show predominance of 2nd and 3rd harmonic. However, harmonic distortion is a funny beast, sometimes it can manifest itself as presence, sometimes as warmth, and often as fat bass, very dependent on the material, so I'm not surprised at the sometimes apparently contradictory reactions depending on the musical source. Distortion is compression, it can subjectively soften dynamics, but when it's enhancing a range, that range can seem louder and counter intuitively dynamics can appear to increase.

There is enough evidence here that the Pass is the more robust amp and technically the more dynamic of the two amps. We also present some interesting evidence that if you adjust EQ for a headphone, be sure to pick the amplifier you are going to use with this EQ. In fact, when EQ was applied, suddenly one amplifier seemed to take on some of the personality of the other. Harmonic distortion can sound a lot like EQ.

In summary, if you like your sound tight, impacting, clear, accurate and transparent with a nice taste of warmth, I would highly recommend the Pass HPA-1. If you like an amplifier that's a bit more forgiving, especially with harsh sources, I would lean towards recommending the Mjolnir. I would not kick either amplifier out of bed!

COMPANY INFO
Pass Laboratories, Inc.
info@passlabs.com
(530) 878-5350

COMMENTS
zobel's picture

$3500 US Dollars for the HPA-1,
Mjolnir 2 ...$849 US Dollars.

You can have four of the Schiits for the price of a Pass, or keep one Schiit and give three Schiits away as gifts, or have one Schiit for every bed in your house, if you really want to have them in your beds. I would Pass on that, and kick either of them out of my bed.

It makes me wonder how either sound next to the Cavalli CTH (sweet tube hybrid with lots of juice)..($250..Massdrop), or the Schiit Jotunheim, which is wonderful in "push-pull" mode..and a monster in power...($399 US Dollars)

You can have fourteen Cavalli amps, or... eight Jotunheims,along with one Cavalli CTH, and change....for the price of one Pass Labs HPA-1.

I wonder too, which would work best with an Aeon Flow Closed, at 13 ohms and 92dB/mW effeciency? ...( yes 13 ohms, just 13 lonely ohms.)

Thanks Bob, for all the info, and allowing me to pick your, (or anyones)..brain here.

geniekid's picture

As stated in the article, the "Mjolnir" is the Mjolnir Audio Pure Bipolar amp ($2100), not the Schiit amp.

That said, comparisons to other amps are always welcome.

thefitz's picture

I would like to reiterate that this amp was not compared to the Schiit Mjolnir 2. I think it's important to pin this down because the comment was made that the HPA-1 is multiple times the price of the Schiit Mjolnir... and that was immediately requested to be compared against amps a fraction of the price of the Schiit Mjolnir. This race to the bottom never stops.

Bob Katz's picture

Hello, Zobel. I paid more than $2000 for the Mjolnir Pure Bipolar so I don't know which model you are talking about. The Pass is therefore about $1000 more than the Mjolnir.

jim in cheyenne's picture

Price is a very important specification to some of us, and the absence of the prices of the two amps here is for me a serious deficiency in the review. While I was well aware that the Mjolnir included here was not the Schiit product, I had no idea what the price of either it or the Pass amp. Including the price obviously would have helped avoid confusion to one reader. I had assumed that the Pass and Mjolnir i question probably were about the same price. The reader should not have to go off on a search to find the prices of the equipment in question.

Based on this review and what other readers have stated as the price, I come away with the thought that the Mjolnir noted is a bargain relative to the Pass--one can buy a lot of music for the $1400 difference! ‘Race to the bottom’ has nothing to do with it.

jim in cheyenne's picture

Price is a very important specification to some of us, and the absence of the prices of the two amps here is for me a serious deficiency in the review. While I was well aware that the Mjolnir included here was not the Schiit product, I had no idea the price of either it or the Pass amp. Including the price obviously would have helped avoid confusion to one reader. I had assumed that the Pass and Mjolnir i question probably were about the same price. The reader should not have to go off on a search to find the prices of the equipment in question.

Based on this review and what other readers have stated as the price, I come away with the thought that the Mjolnir noted is a bargain relative to the Pass--one can buy a lot of music for the $1400 difference! ‘Race to the bottom’ has nothing to do with it.

thefitz's picture

When the above commentor thought that this article involved a direct comparison between a ~$2500 amp and an $850 amp, it was immediately turned into a request for a comparison to a $400 amp. Same breath. And I guarantee you if the request was granted and the feedback was positive, someone would roll in requesting a comparison with a $200 amp. Then a $100 amp.

Headphone folks do this all the time - when the Xiaomi Piston 2 came out, everyone said it was a $25 IEM that sounded like a $100 IEM. So every time a new $200 IEM came out, threads would be flooded with comparison requests to the $25 IEM - since it sounds like a $100 IEM, etc.

That is the race to the bottom, and if you don't stamp it out immediately, it happens.

numbersixx's picture

Er, shouldn't that be Who Is Jill Scott? Words and Sounds Vol. 1?

Bob Katz's picture

you're right, that was the "Who is Jill Scott" album. My bad.

zobel's picture

I think it is important to include prices for items reviewed, along with meaningful comparisons to other units either costing more, or costing less. This comparison gives us assurance that the product's price actually reflects its performance. For the price of the Pass Labs HPA-1, I could buy a very nice used car. I just saw a 2006 Chevy Impala, police package 137K miles, for $3,500.,or a 2002 Audio S4 Quatro...same price.

What 'extra' spending money I have, I wold much prefer to spend on music, than on audiophile hardware that doesn't really fit into any rational scheme of value. I would really love it if reviewers would give themselves and the rest of us a reality check, and cover up the amps being compared so as to eliminate brand bias, and then make listening notes on various cans, not just one model. To really be fair and useful, these tests must include amps across the board in price.

Core's picture

“I would really love it if reviewers would give themselves and the rest of us a reality check, and cover up the amps being compared so as to eliminate brand bias, and then make listening notes on various cans, not just one model. To really be fair and useful, these tests must include amps across the board in price.”

inner fidelity will probably never do this. And I think you know why they will probably never do this. And will inner fidelity do ABX tests of headphone amplifiers volume matched to within 0.1 dB? Outrageous! What do you think this is? hydrogenAudio?

zobel's picture

What I ask for is reasonable. If these listening tests are to have any semblance of objectivity, and most importantly, to be of any use at all to readers.
This review tells me nothing meaningful, actually. Who could be persuaded to hunt up this illusive amp with so little actual information about it that matters, not even considering the enormous price tag, which was never mentioned in the review? Seems a fools game to me.

Core's picture

I am almost in complete agreement with you. This “review” was written, it appears to me, for two groups of individuals—those that might spend 3500 to 130 000 USD on a headphone amplifier and those that, while they may not be looking to buy a headphone amplifier in this price range, are, nevertheless, inner fidelity’s most important readers; for this second group of individuals, this review is, I am convinced, very useful.

xnor's picture

Sighted reviews are like the p-value of statistical inference.
They seem to convey the information that people want to know but actually give you the opposite.

People want to know the actual performance of the device given the test results, but sighted reviews give you subjective impressions (the "sighted test results") given the device.

This is not only backwards, it is fundamentally flawed.

And we've all seen what this leads to for decades now. People praising devices heavily influenced by price tag, prestige ... and then when someone actually listens using their ears (I know, that's shocking!) or measures we find out that the device is performing abysmally.

Bob Katz's picture

If we depended on blind reviews of amps, there would be no sonic difference between Class A, Class AB and Class D, yet critical listeners agree that there are audible differences. I do not perform blind listening comparisons anymore because the subtle differences are simply masked by the noise of the testing procedure. However, that does not mean that sighted reviews are any more reliable or consistent, that is the dilemma. If you do not judge my sighted reviews to be worthwhile or reliable, then why do you read any of them? For your entertainment? Then don't complain. Some people actually respect my opinions, which are more informed, more qualified, and more unbiased than a lot of other subjective reviewers opinions. But I am not perfect, and you must learn to read between the lines. But your knee-jerk reaction recommending blind reviews of amplifiers will simply result in null results for the most part. This goes back to blind reviews showing that amplifiers with 1% THD sound no different than those with 0.001% THD. Why? Because it's extremely difficult and expensive to conduct a valid blind test for subtle differences. And don't try to tell me about your latest casual blind test.... the chances of it revealing a difference when there is one are very slim. The chances of it seeming to produce a null result and concluding "all amplifiers sound the same when at the same level are very high. So who's right? The blind testers? It's the only scientific way to prove. But far more costly and time consuming than you can imagine. I've been there, and done that, conducted some very costly (in time) and successful blind tests, and I cannot imagine doing that for every single review that I publish in Innerfidelity. So quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic. It always will boil down to "subjective tests are bad, blind tests are the only thing, yet these blind tests for the most part reveal nothing but "no sonic difference". Why? Because they are far more difficult to perform than you have any idea, require extreme skill and knowledge to perform right, and can take months to years to reach a valid conclusion.

Enough said. Stop posting about blind tests. For the most part I'm not going to do them for this magazine. If the occasion comes up where it can be done with little cost and time, I may perform one.

xnor's picture

You say that "if we depended on blind reviews, there would be no sonic difference" but "critical listeners agree there are audible differences".

Audible difference means a sonic difference that is perceivable through hearing (that's the ears and not the eyes), so what you said above makes no sense.

"subtle differences are simply masked by the noise of the testing procedure"
I've heard plenty of excuses why not to do blind tests, and none of them have stood up to scrutiny.
What you are effectively saying is that you cannot reliably hear differences.

Then when do you hear them and how do you know?
... right. And that's the problem with sighted reviews.

How do you distinguish "critical listeners" asserting that they hear a difference although they don't and a person actually hearing a difference?

What is the difference between a "critical listener" asserting that some devices improves the sound and a person asserting that globules (sugar beads) cure diseases?

"it's extremely difficult and expensive to conduct a valid blind test for subtle differences"
It may be difficult for reviewers that are used to hearing with their eyes (not referring to you specifically) to actually listen with their ears .. to that I agree,
but it is not expensive.
You again make excuses that are demonstrably false.
Just with a few trials you can actually provide positive evidence for the hypothesis that you can hear an audible difference .. and this is the basis for a review on the sound. Not even for the readers but for the reviewer him/herself, so that he/she can answer the above questions at least with some confidence.

Btw, the magnitude of the sonic difference per se is irrelevant. In simple blind tests we usually don't test for the magnitude of differences, but whether there's any audible difference.

Or are you again saying that the sonic differences are so small, that the reviewers could not tell the devices apart without peeking? Then why do a review on the sound?

"quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic"
Why are you so offended? I have neither brought up the topic, nor have I commented more often than maybe 2 other times over a timespan of several years on this site.

I haven't even suggested that you do a rigorous DBT... After you've calmed down, maybe read my reply to zobel again.

In case you skipped all of this in anger,
tl;dr
Blind comparisons (i.e. listening with your ears) are an invaluable tool for audio reviewers.
In fact, they are the basis for making sensible comments on sound.

In closing, I have to revise my initial statement about the p-value:
You say that "if we depended on blind reviews, there would be no sonic difference" but "critical listeners agree there are audible differences".

Audible difference means a sonic difference that is perceivable through hearing (that's the ears and not the eyes), so what you said above makes no sense.

"subtle differences are simply masked by the noise of the testing procedure"
I've heard plenty of excuses why not to do blind tests, and none of them have stood up to scrutiny.
What you are effectively saying is that you cannot reliably hear differences.

Then when do you hear them and how do you know?
... right. And that's the problem with sighted reviews.

How do you distinguish "critical listeners" asserting that they hear a difference although they don't and a person actually hearing a difference?

What is the difference between a "critical listener" asserting that some devices improves the sound and a person asserting that globules (sugar beads) cure diseases?

"it's extremely difficult and expensive to conduct a valid blind test for subtle differences"
It may be difficult for reviewers that are used to hearing with their eyes (not referring to you specifically) to actually listen with their ears .. to that I agree,
but it is not expensive.
You again make excuses that are demonstrably false.
Just with a few trials you can actually provide positive evidence for the hypothesis that you can hear an audible difference .. and this is the basis for a review on the sound. Not just for the readers but especially for the reviewer him/herself.

Btw, the magnitude of the sonic difference per se is irrelevant. We don't usually test for the magnitude of the difference, but whether a listener can hear a difference.

Or are you again essentially saying that the sonic differences are so small, that the reviewers could not tell the devices apart without peeking? Then why do a review on the sound?

"quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic"
Why are you so offended? I have neither brought up the topic, nor have I commented more often than maybe 3 times in a couple of years on this site.

I haven't even suggested that you do a rigorous DBT... After you've calmed down, maybe read my reply to zobel again.

In case you skipped all of this in anger,
tl;dr
Blind comparisons (i.e. listening with your ears) are an invaluable tool for audio reviewers.
In fact, they are the basis for making sensible comments on sound.

In closing, I can only repeat my initial statement: Sighted reviews on sound are like playing tennis without the net and without the line markings.

xnor's picture
After the first tl;dr just skip to the end.
wbh's picture

H-Y-D-R-O-G-E-N ... hydrogen....hydrogena...hydrogenau....hydrogenaud ...hydrogenaudi...hydrogenaudioDOTorg

Wat up, X?

Greynol and Arnie ain't fun no mo'? Bored ova dare, huh. Me too ;)

Oh, and uh, one mo' thang ...

https://youtu.be/IDDEpnjgTyw

buckchester's picture

I'm with Xnor on this one. If you must know which amp you're listening to in order to tell a reliable difference, it begs the question: can you reliably tell the difference?

Many people who are reading these reviews are expecting to get to truth on these products. If you're not telling them that you'd be hard pressed to notice any difference in a blind test, then I'd argue that you aren't being completely up front with them. I would furthermore encourage people like Xnor to reply and point this out, since you didn't.

And a blind test doesn't have to be as exhaustive as you are insinuating. I would argue that any form of blind test is better than none at all.

Bob Katz's picture

"I would argue that any form of blind test is better than none at all."

Here is where we have to agree to disagree. I've been trained on how to conduct blind tests by two of the world's experts, psychoacousticians in fact. These people do not take their responsibilities lightly. I'm sorry to have to break the news to you: There is no such thing as a "casual" blind test.

Expert listeners are listeners who have either trained themselves or been trained to hear sonic differences which many others say they cannot hear. Therefore, Blind tests on subtle differences may require months of training, an expert trainer, and many trials in order to reach a statistical conclusion.

That ain't gonna happen here, at Innerfidelity, let me break the news to you. And I'm not going to conduct anything less than a proper blind test, with the proper protocols, which requires far more expertise and training than you can imagine. To touch the surface of it, you can read up a bit about the protocol "BS.1116". Google it. One of the cautions by one of the authors of the protocol (who is one of my mentors on blind testing, by the way) is that this cannot be taught by "reading the manual", even though the protocol has been delineated. It also requires training and mentoring.

So I am humbled as we all should be by this dilemma: A casual blind test on a subtle difference is almost always destined to fail, to seem to show that there is no audible difference. We've seen this again and again. Does this mean that there is no audible difference, or that the listeners have not been properly trained to hear the difference, or that the method of the test was insufficient to allow them to hear the difference.

It's a dilemma that continues to trouble me in particular, as I'm currently in a debate about a subtle technique which hundreds of trained audio professionals work with every day, with the premise that we CAN hear and operate on that subtle difference. But the naysayers claim that such a difference should not be audible. Furthermore, blind tests on this difference have so far come up null. Imagine if you were a working professional who has used a particular technique for decades, each time coming up with a useful result to your ears, and your technique has been questioned by others (perhaps not so expert listeners).

So, please rest.... give the topic some rest. I'm quite sincere in my reviews, I've been at it for many years, but you're not going to get a blind test from me unless you can pay my salary for a year so that I can devote my entire energies to a proper, non-casual blind test on the topic at hand. I'm sorry, it's not going to happen.

Read more at https://www.innerfidelity.com/content/katzs-corner-episode-24-pass-labs-...

buckchester's picture

Bob, I appreciate and respect your knowledge on all this stuff. I enjoy reading your columns. However, on the subject of blind testing I find myself disagreeing. While I would agree that if you want to have scientifically valid information it is crucial to follow a very specific set of standards that may be difficult to execute. But it seems to me that a sighted test would contain all the same flaws that an imperfect blind test would contain, and more.

What is the harm in following similar procedures that you use in your testing, with the only exception being you don’t know which amp is which? That wouldn’t be difficult to do at all.

Perhaps:

-Set the volume of each amp at as similar a level as you can (to avoid having to adjust during the testing, thereby revealing which one is which)

-Have someone set one as “A” and the other as “B”. Have that same person change what is “A” and what is “B” a few different times.

Something like this seems simple enough. And while it wouldn't necessarily stand up to the scientific method to be considered statistically valid, I still think it could provide more valuable information than a sighted test.

If you did something like this, do you think you could reliably tell the difference between the two? If not, then surely it begs the question: is there any difference? And if there is, is it possible that difference is too small to meaningful?

I know where I stand: if I can’t reliably pick out differences between two things without knowing which is which, than any differences that exist are too small to be meaningful in any way.

Now that I have your attention, a separate topic: I have been wondering if you are ever going to do a review on Sonarworks EQ. I would be interested to hear your opinion on it. I tried it out. I thought it sounded off at first, but now I absolutely love it and would never go back.

Bob Katz's picture

Thanks for your kind words. In my lifetime I've performed and participated in a few carefully-prepared and matched blind tests and for subtle differences they usually come out null. I have studied how to perform blind testing and taken lessons from two of the world's experts, who are both very quick to point out that blind testing must be rigorous, require great preparation and trained, experienced testers as well as trained subjects. So I humbly usually refuse to venture into that world, and I will not perform a casual blind test, which is the vast majority of blind tests that you have heard about.

One exception was a test of jitter with 20 to 30 participants that was very enlightening. The amount of preparation required weeks, dedication from myself and a partner and rounding up many participants in order to get a statistically-meaningful number of trials. It's not easy, despite what so many blind test adherents claim.

So it either means that there are no sonic differences between things that I hear sighted, OR that the resolution of the blind test (for whatever reasons, including method, training of the tester, training of the subject, inadequately-chosen musical samples, etc.) is not sufficient.

So 'll wait till there's an issue worth arguing over, because a rigorous blind test of subtle differences requires many trials, can take weeks to months, require proper training of the subject(s).... Even then I've seen these fail more often than not. You bring up the question that if the difference is so tiny, why is it worth arguing over, and I respond that I believe the resolution of a blind test is often an order of magnitude worse than actual human perception. Now that's not a claim that I can prove, but it is also not a claim that advocates of blind testing can disprove! It's just a hypothesis that I have.

So those who advocate strict blind testing make their arguments and those who advocate or perform sighted testing make their arguments. Of course I subscribe to scientific method most of the time, but I am also an artist. In my column I choose to express my sighted opinions. Hopefully they seem sensible and reasonable to you, but if not, hopefully they are entertaining :-).

I've been resisting Sonarworks for some unknown reason, eventually will look at it for this column. I have my own research on headphone correction that's getting closer and closer to reality and wish to perform that first.

wbh's picture

xnor:

You sound like card-carrying member of HYDROGENAUDIO.

Most of the so-called 'science-based' discussions -- at that putrifying palace -- are about as useful as a turddy toilet.

xnor's picture
Cute.
Vic's picture

Blue Book pricing on both cars you mentioned starts in the $5000 range. If you find them for quite a bit less than that..... they probably have major issues.

Not to mention the comparison is absurd from the start. For $3500 I can buy a really nice dog. That companionship they will bring is worth far more than any headphone amplifier. It could also feed a homeless family for at least several months. Again, all pointless comparisons, just like yours.

If I might ask an important question. Why do you bother posting here? You seem to actively dislike every review you've ever commented on, so why not do yourself a favor and find another site? I'll never understand this mentality. I don't go hang out on NASCAR forums or sportfishing forums complaining about how I dislike those "sports". It kinda feels like that's what you consistently do here.

zobel's picture
zobel's picture

What a review! It is the responsibility of a reviewer to find the value of equipment being reviewed. Tyll does an excellent job of this, and avoids reviews weighted towards price tags, meanwhile making fair comparisons between cans, regardless of cost.

The thing I respect most of any reviewer is an ear to value. What does the product provide for your money? Tyll constantly keeps the highest performing headphones on top of his wall of fame list, but will kick off the poorer values in head to head comparisons, all else being equal.

Many of the products Stereophile recommends are not even close to good enough for the money, and are often out performed for less money. I think this is no doubt true in this headphone amp recommendation. Therefore, it is just a tire kick.

Vic's picture

Just like my comment to XNOR above, why do you hang out here when you seem to loathe so much of what is written on the site?

Also, you are basically saying "some other magazine often recommends gear which I feel is not the best value. I bet the same thing applies here." What a useful comment! Thank you for sharing your expert opinion, random internet guy!

zobel's picture

If you have an opinion, why not express it? I already expressed mine, and shared what I like and don't like. Perhaps you could read what I've posted with an open mind, or at least read it at all, before commenting so snarkily.

Vic's picture

My issue is why people like you and XNOR bother visiting this site, since you very obviously have long-standing complaints about the nature of the reviews. It's like going to a NASCAR forum and being mad that they never make right turns.

Pages

X