Goodie or Gimmick? The BSG Technologies Reveel Signal Completion Stage for Headphones
BSG Technologies reveel ($119)
Boy, spend a little time reading listening impressions and reviews around the webs and you just walk away shaking your head...opinions are all over the place with this gadget. Let's first talk about what it does.
How reveel Works
While BSG Technologies have patents on this device, the basic idea behind it has been around in audio for a long time. Central to this idea is that while a stereo signal is normally thought of as having left and right channels, it can also be thought of as having sum and difference channels. It's probably easiest to start with the mid-side microphone technique.
In this technique an omni-directional mic (cardioid mics can be used) is used as the mid mic and contains all the center channel or mono information. The figure-8 mic is placed as close as possible to the omni mic, and picks up sound to either side. A positive pressure wave from the left side will produce a positive going electrical signal, but a positive pressure wave from the right will produce a negative going electrical signal. Therefore, when you mix the mid and side mic in polarity you get information from the left of the mic pair, when you mix the mid mic with the figure-8 out of polarity you get information from the right side of the mic pair. The beauty of this type of mic technique is that you can adjust how wide the stereo image is by varying the ratio of mid to side mic used in the mix: more mid for a narrower image, less mid for a wider image. Also, when the left and right channel is mixed together the difference signal perfectly cancels creating ideal mono compatibilityperfect back in the day for AM radio.
The not-so-obvious thing here is that you can take a normal stereo signal and create mid-side signals, though in this case they would be called sum and difference channels. Audio engineers have been doing this for a long time in order to manipulate the apparent stereo image width of recorded material. In addition to simply varying the level ratio between sum and difference channels, you can also equalize and/or delay one or many copies of the difference channel creating frequency dependent alterations of image width. In John Atkinsons review of the $2395 BSG Q0l Signal Completion Stage, big brother to the reveel, he points to a 1986 Studio Sound article on the "Blumlein Shuffler" as an example of how this idea is used in the pro audio world.
The above images show the control panels of three different professional audio tools using the mid-side matrixing technique to adjust apparent width of the stereo image. The top and bottom panels are computer programs the acomplish the manipulation digitally, the middle control panel is a module for a Neve mixing console available as an option, and accomplishes its task in the analog domain.
The BSG Technologies reveel is a similar sort of device. It is a fully analog device that uses op-amps (ST Microelectronics V914i) to perform summing, differencing, phase, and filtering operations on the original left and right channels to essentially enhance the stereo signal. The following simplified circuit diagram from their patent shows what's going on.
Left (35) and right (37) input signals are passed through input buffers (36, 38) And fed directly to the output mixers (40, 41). Left and right signals are also fed to buffer amps (52, 53) which feed a system to create L-R and R-L difference signals, which are then summed with left and right channels again, and then sent to the output buffer to be mixed in with the direct channels. Left and right channels are also sent to a summer (42) to create a mono signal, which is then fed to both a high pass and low pass filter (46, 43) to create a mono bass and treble channel. Channels are then fed to phase adjustments (47, 44) which alter phase about 90 degrees according to the patent, and then to bass and treble gain adjustments (48, 45) before heading out to the output buffers. The patent claims that these frequency altered mono channels provide another "phase layer" of information.
It seems to me, in my layman's reading of the patent, that BSG's claim to a patentable idea is in the mixing of these various channels using the Golden Ratio. A good chunk of the patent details the use of this ratio in the various mixing of signals. BSG Technologies would like to have us think of it in this way (from their BSG Tech website regarding the q0l):
BSG Technologies has developed a method of retrieving sonic information from audio signals that provides a realistic and complete rendering of the original acoustic event. q0l is NOT a processor; it does not synthesize a signal or alter the natural sensory information in any way. Instead of "adding" a host of processing techniques intended to create "effects," we have simply found a way to extract information already present in recordings, but otherwise hidden in conventional reproduction. Our technology enables COMPLETE capture, transmission, and reproduction of such information, including elements that, until now, have remained hidden and buried in electronics, and unavailable to the listener. The result is an audio experience with fullness and richness beyond comparison and one which carries essentially all the dynamic, tonal, and spatial content of a real sonic event.
Technically, I don't buy it. If the recording engineers wanted that sound added to the track they would have already done it. And "an audio experience with fullness and richness beyond comparison and one which carries essentially all the dynamic, tonal, and spatial content of a real sonic event" is a statement that ignores the fact that a recording is and will never be like "the real sonic event." While it seems to me a perfectly legitimate technique for recording engineers to have up their sleeve as they paint their sonic pictures, it doesn't seem to me logical that a particular setting of the various parameters of the circuit, golden or not, could possibly be a cure-all for better stereo imaging and ambience retrieval on all recorded material.
However, I don't listen technically, I listen subjectively, and that means I simply gotta hear the thing for a while to see if I like it. And I did...sometimes. Flip the page for my impressions.