Is a little (of the right!) distortion a good thing?

[Geoff_T]

Hi

In the thread about the piccies on my site was a discussion on whether audio quality had improved in the last 30 or so years.

Issues covered included the consequences to the sound recorded onto a CD because of the ~96dB/oct low pass filter at around 20KHz pruned the harmonics off frequences in the audio band. Despite the hype put out when CD's were introduced, the medium may have lower noise and distortion but sure as eggs is eggs a CD won't sound as nice as a vinyl of the same material.

In terms of numbers, audio performance has improved enormously. Taking Neve consoles, the noise and crosstalk figures on 51 and V series is vastly improved (quasi balanced bussing) on the figures you can get on a (constant impedance, voltage summing) vintage Neve... but which sounds nicer? A rhetoric question!

Money talks with production engineering and the choice of components, especially IC's, might be more governed by the predicted market price of the device than for performance or sound. There's exceptions to every rule...

So why are the 1272 and 1073 circuits ripe for cloning rather than a later and far more high performance IC based circuit?

Could distortion be a lovely thing?

[Dave Martin]

Of course, if it's the right distortion.

[Jim Williams]

Take the common TL072 opamp. Used for decades in English consoles, I found this chip has just the right type and amount of distortion........ that's why I use it in my fuzztone!

Jim Williams
Audio Upgrades

[jbuntz]

Something I've thought about alot actually. Triodes pretty much exclusively generate even harmonics. The 2nd harmonic is you probably know is the octave and is always musically related to the note played. The 3rd is the octave and half and may or may not be in the scale. The more spectral material this is not musically related to the fundamental is just more white noise vail to listen through. The extreme example of it is the dramatic reduction in clarity on a heavily distorted guitar. You can't play complex voicings and hear what's going on very well and it creates all sorts of interesting but unmusical intermodulation distortion.

Geoff, I was wondering something about the neve preamp design. Normally transformers generate primarily 3rd harmonics but the DC across the primary winding on the output tranny will add some 2nd too since normally the bilinear transfer curve is symmetrical (looking at the integral of the signal) but the DC shifts the symmetry so that negative values distort sooner...are my assumptions wrong?

[Geoff_T]

Originally posted by jbuntz

Geoff, I was wondering something about the neve preamp design. Normally transformers generate primarily 3rd harmonics but the DC across the primary winding on the output tranny will add some 2nd too since normally the bilinear transfer curve is symmetrical (looking at the integral of the signal) but the DC shifts the symmetry so that negative values distort sooner...are my assumptions wrong?

Hi

I don't claim to be a transformer expert but the onset of distortion from the biased transformer is adjusted to ensure that the point of clipping/saturation is equal on both ends of the wave.

I think that you can compare transformer bias, in basic operation, to tape bias. You can't efficiently magnetise the particles on the tape unless you apply a bias... usually an ac tone but you'll find on really cheap cassette recorders they even used dc bias.

The 70mA or so dc passing through the primary of the LO1166 biases it to a nice point on its magnetising curve and the audio is modulated on top of this. Whenever I look at the 283 circuit it always reminds me of the sort of amplifiers that they fitted in old record players. The ECF triode/pentode combination where the triode is the pre in front of the output and the pentode drives the transformer.

If you look at really early Neve circuit diagrams like the B100 and B104 you'll see that Rupert drew his transistors so that they looked like valves with the base a horizantal line through a circle (like a grid)and the emitter, an arrow rising at 90 degrees through the bottom of the circle to meet the base in the centre... rather like a cathode.

I think that valves were an influence in the early days.

[tINY]

Originally posted by jbuntz
Something I've thought about alot actually. Triodes pretty much exclusively generate even harmonics. The 2nd harmonic is you probably know is the octave and is always musically related to the note played. The 3rd is the octave and half and may or may not be in the scale. The more spectral material this is not musically related to the fundamental is just more white noise vail to listen through. ....

I wonder if that 3rd harminic would be less objectionable if we still expected to hear instruments tuned to the pythagorean temperment?


-tINY

[barefoot]

Originally posted by Geoff_T
Despite the hype put out when CD's were introduced, the medium may have lower noise and distortion but sure as eggs is eggs a CD won't sound as nice as a vinyl of the same material.

This is such a tired old debate, but I guess I'll take de-bait.

Whenever I listen to vinyl I feel like I'm child again, sitting at the kitchen table in my Irish great grandmother's house.

"How about a little Dave Brubeck?"
"Sure grandma!"
"Let me put a little butter on that for you dear."
"Uh, ok."
..... swalpf.
"And would you like some Radiohead now?"
"Yeah!"
"Here, let me just slather some butter on that for you dear"
"Uh, no thank...."
..... swalpf.
"How about some Koma+Bones for dessert?"
"Yes please!"
"And here's a nice bid dollop of butter for that dear"
"No, I don't want any....."
..... swalpf.
..... swalpf.
..... swalpf.

To my ears, a well-produced recording on digital media blows vinyl away. It's a more open medium and offers far more flexibility to make a recording sound a good, or bad as you choose.

Thomas

[Ted Nightshade]

As far as I can tell, the clean -clean -clean stuff sounds great at real-life performance playback levels, if you can manage that clean- not often.

For lesser playback levels, sounds better to have exagerrated harmonics, more like the actual amount of harmonics from the live music at the actual live level.

[Ted Nightshade]

Insufficient playback level is a form of distortion- we tend to forget that.

[tINY]

Originally posted by Ted Nightshade
Insufficient playback level is a form of distortion- we tend to forget that.

Never thought of it that way... I'd agree with you as long as we are talking acoustic power with a limited room size.


Yamaha tried to counteract that with a "loudnes" dial on some of their units (late '70s?). It worked in concert with the playback level knob to add eqalization based on output level vs "zero" level.

...Dammedest thing, though. when SPLs get past about 100dB, I can't hear as well. Perhaps there are some middle/inner ear non-linearities that get bad at that level.



-tINY

[Ted Nightshade]

The "loudness" controls have more to do with the Fletcher-Munson curves, and are not really about harmonics.

There are lots of good reasons to monitor and listen at "insufficient" (below real life perfomance) levels- for one thing, a lot of musical instruments are quite loud and can be literally deafening to listen to at close quarters in person, especially with room reflections. Some are loud enough to be deafening at some distance, as well! And of course most playback will be quieter than live sources due to insufficient capacity of the reproduction system, so yes, some of the right distortion in the form of harmonic generation can be a good thing indeed.

Nonetheless, those who constantly champion the very lowest distortion figures do not seem to regularly acknowledge the distortion inherent in quieter-than-life playback.

[tINY]

I think that the Fletcher-Munsen effect is the largest part of the acoustic-power perception "distortion". Of course, it's fairly easy to study and varies from person to person.

But, if I think you are saying that some added harmonics simulate what happens between the air and the brain at higher power levels.

I don't know if I would buy that straight off, but it would be awfully hard to study. I think that some distortion may just be pleasing to us humans in certain situations. At higher SPL, it may be too much to be comfortable.

But, the bottom line is: If it sounds good, it's good. You catch it on the recording and I'll play it back as cleanly and accurately as I can....


-tINY

[tonymite]

i'm just posting on this thread cos its so interesting ... anytime someone posts a reply ... i will be notified via email this way ... i wont miss anything

[Ted Nightshade]

Originally posted by tINY


I think that the Fletcher-Munsen effect is the largest part of the acoustic-power perception "distortion". Of course, it's fairly easy to study and varies from person to person.

I would have to agree- I guess I didn't consider that those charts represent averages, and that individuals may vary fairly widely in that way... according to the charts, not much is different at the 8K hump at different loudnesses, where I would think a lot of the harmonics would be found- but of course they are found pretty much full band.

But, if I think you are saying that some added harmonics simulate what happens between the air and the brain at higher power levels.

That's pretty close- I'm trying to say that there in the room with the source, the harmonics are more evident than they are on quieter playback, even if they all were captured- so you have to exaggerate the harmonics to get that "there in the room with the source" detail and timbre.

[B]
I don't know if I would buy that straight off, but it would be awfully hard to study.

[B]

Not sure why it would be hard to study...

I think that some distortion may just be pleasing to us humans in certain situations. At higher SPL, it may be too much to be comfortable.

Yeah, I think that's true too. My point was that the super-low-distortion in and out paradigm is only really satisfying at real-life performance levels.

But, the bottom line is: If it sounds good, it's good. You catch it on the recording and I'll play it back as cleanly and accurately as I can....


-tINY

Much appreciated! But I still have to look out for the majority of folks who will play it back pretty much any old way...

[tINY]

Originally posted by Ted Nightshade



Not sure why it would be hard to study...

It would be hard to study because it is a perception (unless you can monitor synapse response from the inner ear) and it is secondary to the F-M effect. You would have to null-out the frequency response for each individual for various levels and then devise some subjective matrix for quality of different levels.

Until it hurts, "louder" is almost always subjectively better to most folk. Did you ever notice how compressed pop albums are any more (and how much more FM broadcasters add)?


-tINY