The bark fix

September 21, 2021
 by Paul McGowan

In a recent post, The Bark Syndrome, I identified a problem that is difficult to pinpoint its source. Barking voices.

You’ve no doubt experienced on multiple recordings the bark of a loud voice. The signer gets going and suddenly you wince. Your face scrunches.

Where in the chain does this change in quality occur? If we look at the raw waveform for signs of clipping or dynamic compression, we see nothing alarming.

I first ran into this issue back in the early 70s when Stan and I started PS Audio. At the time, we were building only phono preamplifiers. Those preamps started out life based on an IC op-amp, the venerable 709. It wasn’t long after those first circuits that we became dissatisfied with the limitations of an integrated circuit operational amplifier. Among them was an annoying tendency to sound musical only on softer passages of simple music. Whenever the levels got too high or the music became complex, we winced.

The problem with integrated circuits is the designer’s inability to change anything internal to the chip. The chip does what the chip does.

Our first cure for facial wincing came in the form of a discrete op amp. By using our own discrete transistors and resistors to mirror the structure of an operational amplifier (differential input pair feeding a gain stage whose output fed a buffer), we could solve one of the IC’s biggest problems, that of sounding muddled when the music became complex. We theorized our discrete amplifier was free of this problem because we were finally able to control the IC’s over-the-top high open-loop gain. (What this means is that when an amplifier has extremely high input to output gain to the point of instability without resorting to feedback to lower that gain to something useful, we tend to suffer from the problem I described earlier of complex music becoming cluttered. By ensuring the amplifier’s gain structure and speed are capable of stable operation at high gain without the necessity of feedback, much of this problem is no longer heard by the listener).

Now, with the clutter problem solved by the use of a discrete circuit in which we could control the circuit’s gain parameters, our next challenge was the Bark Syndrome. That had unfortunately remained and was for a long period of time a real head scratcher. Why, when the maximum output signal the preamplifier had to deal with was a mere 2 volts (and our circuit could easily output 7 volts without any increase in distortion), did signals approaching that level tend to make our faces scrunch?

On a whim, we decided to see if it might be something we could not yet measure. Headroom or more accurately, exceeding the linear region of the circuit. Because we had moved away from fixed integrated circuits to a discrete version we were no longer bound by the power supply limitations of the chip. (Integrated circuit operational amplifiers are typically limited to +/-15 volts on their power supply rails).

Easy enough for us to rejigger the power supply rails to double what we had been using. Now, with +/- 30 volt rails we played again the same passage of music that had formerly been barking. Voila! Less bark and by a rather noticeable margin.

Just a bit of history for you to consume.

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11 comments on “The bark fix”

  1. SPL Audio uses 120 V for their Voltair technology. Similar the high volt series “HV” from T+A Audio. And haven’t vacuum tube designs even higher voltages and a larger linear range with even more benign clipping behavior and only even (!) harmonic distortions?

  2. I haven’t been able to have a chance to comment in yesterday’s post, but this new and wonderful one from you Paul will be highly relatable. 🙂

    I’ve long since been sensitive to vocal sibilance and extended or exaggerated treble response.
    I have a pair of HD 800’s made by Sennheiser and they pick up any or overly extended “Bark” in a recording and the 800’s are kind of like my truth sayers just like how you shuffling around those power supply rails really revealed something to you.

    It is important to know that a lot of mishaps I hear in audio recordings is not because of my system. At least not now. 😉
    Anyhow, I love this story Paul. You’re an incredible troubleshooter and I really enjoyed your story of how you sifted through the problem to get rid of the screech. 🙂

  3. This posting, is directed to Paul!
    When I was about perhaps maybe 13 or 14, that was the first time I heard an amp that used either bipolar junction transistors or j-fit transistors.
    I think I understand what you mean, when you talk about the barking centrum.
    I’ve heard stereo receivers made by both Scott and Pioneer.
    But of Corse, these are receivers that were made in the late sixties and early seventies.
    The barking centrum didn’t find its way in to those receivers.
    The first receiver that I heard that had j-fits in it, was made by SONY.
    But I didn’t care too much for its sound.
    The thing added a lot of noise to the music when you turned the volume up a little too high.
    The same thing was also true about a Technik’s receiver that I got my hands on, daring 1986.
    This is the one that had bipolar junction transistors in it.
    It was far worst then the SONY that used j-fits.
    For awhile, I went back to my JVC that uses mossfets in it.
    I didn’t get any of the barking centrum when I cranked the volume just about all the way up.
    What was done differently in 1974 aposed to what was done in 1985 and 1986?

  4. I’m not technically adept to understand the difference between operational and discrete amps, but your post makes me want to do further study. I do know that I judge any audio component (be it source, amp, loudspeaker, or cable) on its ability to handle complex passages at both low and high volumes, without bark, sibilance, slurring and other kinds of unnatural distortion. Large orchestral, choral and pipe organ works can only be successfully rendered by exceptional systems in which every component is up to the challenge.

    1. On second thought, why should I do further study? I’ll just let the audio circuit designers solve those kinds of problems and enjoy the fruits of their labor 🙂

  5. I’m actually afraid that my ears and head resonate at a Norah Jones and piano frequencies like 500/1000hz…it can still be a comb filtering thing which is still going to be a challenge but easier than getting new ear drums. Wish me luck.

  6. In the old days I made the same experience like Paul, OPAMP’s sounded harsh and barking. That’s why I build transistor mass graves instead of using a few IC’s. Nowadays operational amplifiers like OPA1611 reach a quality that there is no reason to reject them in general. IMO barking voices are more likely a problem of mid range resolution, respectively quickness of the speaker and the room itself, keyword waterfall diagram. A loud passage of a female voice can sound barking on the first stereo system while it sounds throaty exhausted through a more resolving one.

  7. We have known for nearly 50 years about overloading intermediate gain stages with slow output devices (TIM), thanks to Matti Otala. What has only been published recently is that REAL music (on stage) of many genres including pure acoustic performances have transient peaks of +18dB in the top octave, that are not registered by VU meters or VU algorithms. Even most peak meters won’t register a one or two sample peak.

    https://m-noise.org/

    These peaks are less common in studios with dead walls, gobos, iso booths, engineers twiddling knobs, and players wearing headphones for a variety of reasons – but can occur in situations where there is significant room sound and zero processing, because processing phase shifts the peak components and reduces the crest factor a lot. Use of supersonic microphones also increases the bark risk.

    I record in DSF, set level below -15dBFS and still use a peak limiter to prevent digital overs. This reinforces the inadequacy of 16 bit formats. If you allow 18dB headroom, the other 99,9% of the music is 13 bit resolution, 7-10 bit waveforms for quieter passages.

    Then there is another source of “bark”: non-linear diaphragm breakup and cabinet resonances. I have been researching this for guitar speakers. They have designed in cone breakup to voice the amplification for electric instruments, and it varies a lot depending on volume level.

    Especially stiffened cones and metallic domes exhibit this distortion. If you look for the bobbles on un-smoothed raw driver fr and impedance curves, you can see cone breakup at 1 Watt. It is going to get worse at higher power.

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