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 compatibility—perfect 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.


Control panels for three professional stereo width control systems using mid-side matrixing. Top - Voxengo MSED; Middle - Rupert Neve Stereo Field Editor; Bottom - Algorithmix K-Stereo Ambience Processor.

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.


Inside the all analog reveel one finds three ST Microelectronics V914i quad op-amp chips among other components.

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.

BSG Technologies
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Byrnie's picture

I'm not trying to nitpick but help out.  I noticed you used "though" when you meant "thought" a few times in the second paragraph.  Great article!  I can't wait for your 1540 review!  I hope all is well!

Tyll Hertsens's picture

Fxt, thanks.

Got quite a few things in for review, the 1540 is maybe 4 or 5 away.

markus's picture

On a portable player with a custom rockbox firmware, you can adjust the stereo width in percent. Values above 100% will progressively remove components in one channel that is also present in the other. This has the effect of widening the stereo field. A value of 100% will leave the stereo field unaltered.

What do you think of that, Tyll? Isn't this the same effect?

bogdanb's picture

maybe I am wrong. maybe i did not get it, but if I did, I might be right with the suggestion I am about to make:

Could you record the from the headphone output of the device to a computer an then post a sample of the effect on and off for us to understand the device. 10-20 seconds would be enough (something free of copyright)

Since it is not a headphone or a sound producer (speaker, amp, dac), but a sound mixer in a way, I think you could let us listen to what it does and explain even more if you think it is necessary.

MacedonianHero's picture

Hi Tyll:

Are you going to measure this amp's performance?

DrForBin's picture


i remember long, long ago when Klipsch was touting the ultimate 2 channel speaker set-up to be a pair of Klipschorns for the left and right channels with a Cornwall in the middle playing a mono signal. at least now it fits into your pocket instead of taking up a 16' wall!


GNagus's picture

Is there a type of headphone (closed, open, brand, impedance, etc) that this device works best with?

RPGWiZaRD's picture

So would you say this is like a hardware stereo image tweak with only one fixed setting?

It's a shame they don't offer an ampless/gainless mode and just let it run through the filter that does the stuff it does, it probably increases the noise floor quite a bit and I reckon it could become a problem from noisy sources or if you'd want to use your own amp with this, especially with portable setups/IEMs.

I agree with you on the "one-size fits all" argument, I'd also greatly prefer some configurability to increase its usefulness. One size fits all only works in the Apple-world, which is why I'm not part of it. 


dAd's picture

I did get to hear it briefly at a friends house.  I heard the gain difference and the additional ambient info pushed up front on the two tracks when I did a bypass comparison.  The effect was iinteresting yet I felt like I was hearing less of a black background and more noise along with the additional info.

I did notice a widening of soundstage on both cuts and a ever so slight loss of focus or imaging on some instruments.  They got bigger and less defined in space.

Would love to spend more time with it to fully develop an opinion, but for now more important things to listen to for me.

AGB's picture

This was Tyll's most important observation:

"... a recording is and will never be like "the real sonic event."

It is true for too many reasons to list here, Tyll's is a great observation.

Electro-mechanical devices do not hear or speak the way organic devices will; their "understanding" and conversion of the dimensonal aspects of sound does not resemble how organic devices, live instruments propagate sound or how the human ear hears.

I am not saying the problem cannot be overcome, I am saying it is not likely to be entirely overcome, and if ever, not soon.

This device seems to be some sort of crossfeed manipulator, no big deal, DSP technology already does the same function in the digital domain far better, and it's only time before the better technology will be incorporated into DACs or other discrete chips.

Some music players already have a similar technology, DSP-based, albeit the effects will not be exactly the same.

Fidelia - resampler and music player - has FHX, a headphone module that does more or less a similar trick...but it is natural entirely, and will not make one uncomfortable.

I never need to turn FHX off, it works.

Reticuli's picture

I would love to buy a good, inexpensive stereo to mid-side box. I tend to think M-S is the best format for stereo listening, particularly in live PA setups of pre-recorded music or DJing.

TechAdventurer's picture

I love listening music every time I travel - but every time I need to take with me the charger of the phone, also of the amp - is there a model that is without battery - to use the power of the phone for example?