"The Audio Critic" Subjectivists v Objectivists or The Blind Misleading The Blind - Page 3

I cannot (offhand) think of any parameters where 10% error would still be considered High Fidelity , but if you have some references I can look up I would be interested in reading further, seriously.


I have been trawling though the AES library and I cannot find any backup for that, I have heard this in the past but I am not sure that this is not an urban legend put forth by SET amp manufacturers, again I would be interested to read some more about this. Also surely this is only a problem if you overdrive an amp, if you keep an amp within its comfort zone distortion should not be an issue with any design ?

More generally , I think it resolves down a number of issues, namely what do we mean by HiFi as regards measurements(1) , is there any correlation between measurements and perceived quality(2), what can we actually detect in terms of deviation from some technical ideal(3) and as you suggest what is worth measuring in the first place(4).

1 - If measurements are important then they should reflect no (or the smallest possible) change to the input, for an amp we used to say a wire with gain for a CD player a flat FR and inaudible background noise.

2 - Probably only in egregious cases - see tubes and LP

3 - Pretty well documented in the psychophysics literaure

4 - Those which support meaningful comparisons between items. Comparing the noise levels of CD players is probably meaningless except in pathological cases , ditto channel separation, dynamic range, SNR and speed stability, for LP systems these are meaningful comparsions.

To be accurate, Sound & Vision was the result of the merger of Stereo Review and Video Review Magazines. But you are correct, High Fidelity, Stereo Review, along with Audio Magazine as well as the original Sound & Vision magazine published in Canada, shared many contributing editors and writers along with a common objective editorial philosophy.

That is a sad state of affairs.

This is not a myth. There are plenty of academic papers on the perception of nonlinear distortion. Start with:
D. E. L. Shorter, “The Influence of Higher-Order Distortion Products in Non-Linear Distortion”, Electronics Engineering, April 1950
and have fun from there. For fairly recent stuff, look for papers by Moore et. al. and Geddes.

Because the ear is so effective at filtering even harmonics, total harmonic distortion is essentially meaningless. It's the distortion profile that matters.

Once the threshold of audibility is reached (which varies by harmonic and by even/odd), odd harmonics contribute to a subjectively brighter sound, while even harmonics contribute to a subjectively warmer sound. Loudspeaker designers can and sometimes do compensate for this by introducing appropriate linear distortion (i.e. frequency response) nonlinearities.

Practically speaking, this is an easy experiment to try yourself if you have a decent background in signal processing and an hour or so to spend with Matlab or your favorite tool.

Dr Geddes is a frequent contributer at diyaudio.com

diyAudio Forums - Geddes on distortion measurements - Page 1

I believe his current thinking on distortion audibility is that as long as it is not gross and all orders decrease with signal level then any competent (solid state) amplifier is fine - he uses a Pioneer integrated amp to demo his waveguide speakers

Any good amp driven within its limits will have much lower distortion than the acoustic drivers at high levels and any Class A amp should be free of low level distortion increase - its easy for desktop headphone amps to meet both criteria

Another "datapoint": the "gold standard" of analog audio - studio master tapes have 3% 3rd harmonic distortion as the defining "0 dB" recording level - so some odd harmonic distortion isn't absolutely "bad"

Thanks for the references. I cannnot track down the Shorter paper but I did find a few other related papers (Geddes and Lee, Moore and so on) on the AES Library. By and large tube distortion does appear less intrusive than SS distortion , though most tests really do thrash amps in order to get them to distort audibly, I do not do this.

Some of the Geddes and Lee papers were very interesting, in one they showed very weak correlations between both THD and IMD and perceived quality.

Czerwinski et al (2001) have an interesting take on THD and IMD

Good old IMD. My audio arch-nemesis. What do you guys think of memory/thermal distortion? Is it audible? Perrot (of Lavardin) claims it's at least one of the reasons tube amps sound "better": http://peufeu.free.fr/audio/memory/p...easurement.zip. There's also a pretty thorough theoretical analysis on the same site: Memory Distortion Philosophies.

IMO IMD is the most overt type of distortion when listening with headphones. I've yet to hear a single headphone that can play the following IMD test sample at high (but reasonable) volume without clearly audible distortion: http://members.iinet.net.au/~hararghost/IMDtestA.mp3 (the distortion is identical in the .wav version, and isn't in the actual audio data).

What seems strange to me is that whether you play the test sample on full size one-way speakers, IEMs, regular dynamic headphones, or electrostatic headphones, in all cases the distortion occurs at roughly the same perceived loudness (taking into account the fact that distortion will be lower if bass response of the speakers are lower). It seems suspicious to me that in all these different types of speakers, which work by different principles and, in the case of the full size speakers, work at very different volumes, that the distortion occurs at roughly the same perceived loudness. Any thoughts?

While I have no answer to your question, I thought I would provide some anecdotal data. When I play that I hear a tone around 7-8khz, and a periodic thumping. Nothing sounds particularly distorted, but I'm not sure what IMD sounds like, to be fair.

Here's the same file with the 2 parts panned left/right (ie. no IMD) for comparison: http://members.iinet.net.au/~hararghost/IMDtestA2.mp3

Making one's biases clear and open is good science. Everyone has them, anyway.

One can be biased and still do good science. Clarity and openness with their methodology is the key.

That's not easy at all. It is in fact extremely difficult. I know what I'm talking about, I've lead or took part in two double blind tests so far. The first between interconnects, the second between amplifiers.

The first major difficulty is to find a room. Our first test took place in a hifi shop while it was closed, thanks to a salesman who had access to it. The second took place in the listening room of a dealer, who had it separated from the shop. It took more than one year between the listeners being ok to meet and bring a given list of amplifiers, and the day the dealer proposed to host a blind listening test.

The second difficulty is to adjust the amplifiers levels. Same problem (even worse, since there is no volume setting) with CD players. With many amplifiers, this is plainly impossible because the volume is only adjustable by steps of 1 dB, while a precision of 0.1 dB is required for blind comparisions.
The level measurment is extremely difficult in itself. A voltmeter or an oscilloscope are useless, not talking about a sonometer, because none have the required precision, except very high end voltmeters... don't forget that we are measuring alternative voltage, not direct... Standard voltmeters do nothing less than 230 volts in alternative mode (that is, if you don't go too high in frequency above 50 Hz !).
A soundcard can do it, if you feed it with the speaker output, but unless you have strong XLR plugs, the soundcard jacks are likely to cause short-circuits, that can blow the amplifier out, especially expensive ones, that seldom have the basic protections against it.
And don't forget that you must measure the speaker output while the amplifier is loaded, since a low damping factor is likely to cause a voltage drop higher than 0.1 dB when you plug the speakers on !

Third problem, you talk about 13/16 being a success... that's a 1 percent chance of guessing. For many sceptics, the odds for two amplifiers that measure well to sound different is just 1 percent. Guessing or sounding different is thus equally likely ! A proof would require a probability of guessing equal to 1 percent squared, that is 1/10 000, therefore a minimal score of 16/16 !

Then, one isolated success is not a scientific evidence. The result must be reproduced.

Then, if some people fail because a musical sample, or a given speaker model, is not discriminating enough, you get the problem of the meta-analysis : the successes become isolated among failures, they can then be considered as statistical fluctuations, while they were perfectly significant, taken alone !


Double blind listening test are extremely interesting. They are even very interesting to undergo by oneself even if the result is unconclusive.
But they are also extremely difficult to run properly.

At a given listening level, the thumping begins to disturb the sinewave. Focusing your attention to the sine, instead of sounding steadily held, the sine seems to be attenuated by the thumping.

This suggests that the distortion occurs in the ear, and not in the speaker.

This is comfirmed by the experiment I just ran : I can hear the distortion at a given level in my headphones (HD600) on your file.
I then put off the headphones and carefully listen to them, held in front of me. The sinewave then sounds perfectly reproduced.
When I put them on, still without changing the volume, I can hear the distortion again.

This is consistent with my experience about pop music events. When I am too close to the soundsystem, the music seems very distorded. But at this time, if I plug my ears, I can hear through that the sound is actually perfectly clean. That's my ears that distort.

Another experiment can be run, that should be more conclusive, but I can't do it at this time of the night : put aside both speakers, then play your two files at a listening volume enough for the first one to distort.
If the distortion occurs in the ear, the second one will distort too. If it occurs in the soundsystem, the second one won't distort.

I agree, it certainly would seem that the distortion is at the ear, not at the transducer. However I just did the following with a full size speaker rig: -
-I disabled one of the speakers to ensure stereo cross-modulation didn't occur
-I played the test sample and raised the volume until the distortion was very obvious
-I then inserted earplugs and pressed them into my ears such that the sound reaching my eardrums was equivalent to listening to the speakers (and headphones, in a seperate test) at a low volume at which the distortion does not occur. I did not change the volume - I only attenuated the sound using the earplugs.
-The distortion was as audible as it was without attenuation. This clearly rules out the ear as the cause of distortion.

Earlier I wondered whether the distortion was caused by the output stage of the amp/source (aka memory/thermal distortion) and wrote some software to do short time-domain fourier analysis. I couldn't detect any significant distortion occuring. At low impedance loads, the output caps were being soaked dry, but there wasn't any significant distortion of the high frequency tone or intermodulation products which could account for the huge distortion one hears with this effect at high volume.

It leaves the speaker as possible source of distortion, but does not rule out the ear in all cases. Maybe both cause distortion.

I just tried both test samples with speakers side to side, but my small boomers don't allow me to play the sample loud enough for the distotion to appear.

I'd be curious to hear your reasoning for this. If the distortion was caused by the ear, it would have the same degree of distortion regardless of transducer principle. Also, I just tested on a 2-way speaker where the crossover is at 800Khz (lower than the high tone in the test samples). Regardless of the volume, there was no distortion audible on this setup. These 2 tests rule out the ear as the cause entirely.

Maybe both the ear and the transducer cause intermodulation. Your result could be explained if the ear reacts especially to very low frequencies (with intermodulation).

I have actually observed this several times, in vast closed spaces, like tunnels. I use to hear intermodulation between two distinct sources of noise : the noise of cars running, that is a broadband noise, and infrasonic oscillations around 10 - 20 Hz, that have the ability to drive the noise made by cars into oscillation in my ears when they are strong enough to be "felt" inside the ear.
This can only be explained either by intermodulation in the air, either in the ear.

The absence of intermodulation heard in your last speakers could then be explained by an insufficent level in very low frequencies (your sample goes down to 20 Hz), while headphones can easily reproduce such low frequencies.