BSG qøl Signal Completion Stage Measurements

Sidebar 3: Measurements

I measured the BSG qøl Signal Completion Stage with Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see and the January 2008 "As We See It"). The BSG was non-inverting from all inputs to all outputs, in both active and bypass modes, with the XLR jacks wired with pin 2 positive. The input impedance was usefully higher than specified, at 18k ohms single-ended and 41k ohms balanced. The balanced output impedance was to specification, at 53 ohms at all audio frequencies, while the unbalanced output impedance was much lower, at <1 ohm.

With its matrixing circuitry, the Signal Completion Stage's voltage gain depended on the input signal configuration. With just one channel driven from an unbalanced input, the gain was a high 10.6dB from that channel's balanced output, and 6dB lower from the unbalanced outputs. With both channels equally driven from an unbalanced input but with the right channel in antiphase to the left (L–R), the gain was even higher, at 12.8dB balanced and 6.8dB unbalanced. However, when both input channels were in phase (L+R), the gain dropped to 7.8dB balanced, 1.8dB unbalanced. For balanced input to balanced output, all of these gains were reduced by 6dB.

The BSG had a wide frequency response, its high-frequency output dropping by 0.5dB at 50kHz into 100k ohms, with excellent channel matching (fig.1, blue and red traces). While the output dropped to 600 ohms (fig.1, cyan and magenta traces), the high-frequency extension was not affected. This graph was taken with an L+R input signal. Muting the right input gave the responses shown in fig.2. The left-channel output (blue trace) has risen by 2.82dB, but there is now an antiphase output at –8.1dB in the right-channel output. This suggests that the multiplying factors applied to the Sum and Difference signals in the matrix are slightly different from the Golden Ratio's 1.618 mentioned in the BSG patent, which, by my calculations, would give an antiphase signal in the undriven channel's output 12.5dB lower than the driven channel's, rather than the measured 10.9dB.


Fig.1 BSG qøl Signal Completion Stage, L+R input signal, balanced frequency response at 1V into: 100k ohms (left channel blue, right red), 600 ohms (left cyan, right magenta) (0.25dB/vertical div.).


Fig.2 BSG qøl Signal Completion Stage, L input signal, balanced frequency response at 1V into 100k ohms (left channel blue, right red) (1dB/vertical div.).

These measurements were all taken with sinewave signals, which, with a product such as this, do not truly represent what will happen with music. I therefore played the pink-noise track from Stereophile's Test CD 2 (Stereophile STPH004-2), the first half of which is a dual-mono signal (L+R); the second half has noise that is completely uncorrelated between the two channels. These two noise signals represent the two extremes that will be presented to the qøl processing; the uncorrelated signal was reproduced 3.4dB higher in level than the correlated noise. With music signals, which will have an interchannel correlation somewhere between these two extremes, there will always, therefore, be an increase in level of up to 3.4dB when the qøl signal processing is engaged, which makes A/B comparisons difficult.

Turning to the BSG's performance when used as a line stage, the matrixing circuitry rendered moot conventional measurement of channel separation. The unweighted, wideband signal/noise ratio, ref. 1V output with the input short-circuited, was 72.9dB left and 72.0dB right, these figures improving to 85.3 and 83.0dB, respectively, when A-weighted. Fig.3 shows how the THD+noise percentage in the Signal Completion Stage's balanced output varied with voltage into 100k ohms. The output circuitry clips at a high 19V, while the downward slope of the trace up to the clipping point reveals that if there is any distortion in the BSG's output, it is buried in the noise. Into 600 ohms (not shown), the clipping level was a still-high 16V, suggesting that the Signal Completion Stage has a beefy output stage; again, any distortion present was beneath the noise floor.


Fig.3 BSG qøl Signal Completion Stage, balanced distortion (%) vs 1kHz output voltage into 100k ohms.

I examined how the THD+N percentage changed with frequency at a level, 2.5V, close to the maximum the BSG will be required to deliver in practical use. I haven't shown the result because it was flat with frequency and obviously just noise. As with the measured S/N ratios, the right channel was a little noisier than the left. Fig.4 reveals that this was due to some very low-level power-supply components in that channel. This graph was taken with the demanding 600-ohm load, and a trace of second-harmonic distortion can be seen in both channels. But at –112dB (0.00025%), this distortion is inconsequential. Intermodulation distortion (fig.5) was also very low.


Fig.4 BSG qøl Signal Completion Stage, balanced spectrum of 1kHz sinewave, DC–1kHz, at 2V into 600 ohms (left channel blue, right red; linear frequency scale).


Fig.5 BSG qøl Signal Completion Stage, balanced HF intermodulation spectrum, DC–30kHz, 19+20kHz at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

Finally, although one of the BSG patents refers to a complicated phase-shifting and phase-layering circuit in addition to the matrixing, the Signal Completion Stage's impulse and step responses, and plots of phase and group delay (not shown), didn't indicate any phase shift, either for a single channel on its own or for a dual-mono signal.—John Atkinson

BSG Technologies
3007 Washington Boulevard, Suite 225
Marina del Rey, CA 90292
(310) 827-2748

guitarist8's picture

This certainly seems like an interesting product. However, reading through this review it reminded me of the BBE Sonic Maximizer that I have used in many live sound applications. Any experience with this, much cheaper, piece of gear in a hi-fi environment?

cgh's picture

I heard this device at RMAF11.  I could clearly hear the dB gain and a widening of the stage during the A/B session they gave us.  The people representing the company indicated they really were not into audio -  my inference was that audio was some derivative use.  As someone with a background in research level physics my BS detector normally goes off in these situations, especially when I start hearing unsubstantiated magic beanisms like "quantum" or "tunneling" or or some other high voltage torture that results in the sound being different .... I only remember them talking vaguely about phase.  My BS detector didn't go off.  They seemed genuine, excited about their product - almost giddy - curious about audiophiles, and not really too  aware of the technical details.  I was curious.  

Segue to the latest issue and I got the answer to my question.  This product, regardless of price point, will not be for everyone, especially purists (aspiring?).  But it is nice to have some transparency.  All too often some product is introduced that changes the sound; but is it for the better?  Or do people just get excited when they can hear a change and the marketing sets the stage for its reception being perceived as an improvement?  So thanks to Mr Atkinson and BSG for the transparent and well-written article.

(Edit: p.s. I have a funny picture from their room I saved that is two 'scopes comparing a signal with the device on and off.  Makes sense in retrospect :-)

OneMic's picture

I just had to comment that this is one of the best reviews I have read and frankly I am really glad to see a review of this caliber on Stereophile.   This type of educated and informing review is what myself and many of your readers have been waiting for on these type of "tweak" or enhancement products.  

JA you did a standup job cutting through the manufacture's frankly B.S. copy of "not being an effects box but digging deeper into the recording and uncovering hidden and secret information through our proprietary processing technology".   You explained in relatively understandable terms that this is precisely an effects box with a singular well known effect.  

While being an effect box is not a bad thing, I am just glad that someone at Stereophile is finally calling a spade a spade and not just ignorantly regurgitating the manufacture's fraudulent marketing speak. 

JA, I anxiously look forward to more of these kinds of articules as they do a great job of shining a light of truth on the dank and dirty world of tweaks. 

pwf2739's picture

I am not an engineer nor a designer of reference level audiophile components. I am one who very much wants to hear the reproduced music as lifelike, detailed, natural, involving and as close to live music as possible. Towards that end I have devoted a substantial sum of money to achieve what to me sounds engaging and makes me enjoy the music. 

I frankly don't really understand much of what was written in the article. I mostly skimmed through the reprint of the patent application. I certainly don't have a great sense of what a Blumlein Shuffler is, what it does, or how it may be applicable in today's high end components. I'll leave that for those far more learned than I am. 

However, I have owned a BSG qol Signal Completion Stage for eight months now. I have had professional musicians, recording engineers, audiophiles and friends in to hear my system. In each and every case, the most discussion centered around the qol unit. And each and every person who has heard it, including wives of friends were amazed at the difference it makes. 

When my friends inquired about the qol unit, we did not discuss a Blumlein Shuffler or a patent application. I simply told them that it brings much of the recorded sound to the front that may be ordinarily hidden or obscured. I told them that it made the music sound so much better. Everyone was astounded at the difference it made. Simply put, it makes the music sound more lifelike. Not in the way a graphic equalizer on a mid-fi surround sound receiver does but actually more lifelike. Your hear so much more music with qol. The proof is in the bypass button on the remote- you can actually hear what you are missing without qol. 

I don't really care if my system costs $200,000, $2,000,000 or $2.00. I can tell you that any high end system I build will have a qol Signal Completion Stage as part of the components. 

Patents, Blumlein Shufflers, equalization, this, that- all are fine discussions. For me, I'll take the music. Because qol works. 

neogeo's picture

Next time, please don't make it so obious that your comment was paid for by BSG :)

russtafarian's picture


Your article inspired me to try this out for myself.  After reading your description of the Blumlein Shuffler, I tracked down a free mid-side VST plug-in ( ), installed it in Jriver (music playback software for the PC) and played around with mid-side levels.  I found that a small increase in side level (between 0.8 and 1.2 with this plug-in) did help the soundstage bloom on many recordings.  Too much level and it sounded too phasy and exagerated.  But when set to a tasteful level, it really works!

I heard the BSG unit in a friend's system a few months ago and really liked what it did.  He listens almost exclusively to vinyl so an analog solution like the BSG is ideal for him.  For those of us who have computer audio setups, we have an alternate path to get to the same place.  Thanks for cracking this nut for us.

prerich45's picture

You are correct!!!! You do hear more instruments when cautiously applied! Biggest thing, it  was FREE!!!!  Listening to it in J River now! 

Et Quelle's picture

indecisionIs the variation on already known techs enough to justify the cost.Is it any better choosing effects on a receiver. Buy it if your wealthy, looks cool?