Audio Equipment Distortion

[Verdinut]

What's the use of testing for THD at 20 kHz on audio equipment when the 40 kHz harmonic, for instance, is way beyond the human range of hearing? We're not bats!
In my opinion, unless the usual measured and published THD figures at 20kHz refer to the 1st harmonic of the 10 kHz frequency, it would really be sufficient to limit testing for total harmonic distortion to 10 kHz, and rather concentrate on the other important specs.
Any comment someone?

 

[Bizarro_Stormy]

We're not bats!

 

[M Code]

The same can be said for the low bass @ 20Hz...
Even though the assumed average audible frequency response is like 60Hz to 15kHz, U want the frequency response to be basically flat between 60Hz-15kHz. In order to deliver this, the circuit and/or amplifier needs to be capable of handling extremes beyond 60Hz and 15kHz respectively...

Just my $0.02...

 

[TLS Guy]

What's the use of testing for THD at 20 kHz on audio equipment when the 40 kHz harmonic, for instance, is way beyond the human range of hearing? We're not bats!
In my opinion, unless the usual measured and published THD figures at 20kHz refer to the 1st harmonic of the 10 kHz frequency, it would really be sufficient to limit testing for total harmonic distortion to 10 kHz, and rather concentrate on the other important specs.
Any comment someone?

Not all distortion is harmonic and or linear. However the absence of THD at 20 KHz is pretty good evidence that things are A OK.

Just because the hearing limit is 20 KHz does not mean that trouble around 20 kHz is not audible. It certainly is at times. The most notable example I can think is aluminum dome tweeters. Even the best of them break up violently at 20 KHz or just above. You would think this would not be audible. However many including myself can hear it. It adds a peculiar sizzle to the reproduction that is not highly noticeable, but it is there and enough to put me off using them. Many have noted this.

The other thing is many early CD players had anti aliasing filters that did peculiar things around 20 KHz. This was definitely audible. In 1984 I expended significant funds to obtain a Revox player designed by Roger Lagadec that did not do this. Most early CD players had a problem here and got CD an early bad rap.

So yes, knowing there is good performance out to 20 KHz is a required benchmark.

 

[Speedskater]

How humans perceive distortion does not relate well to THD numbers. Yet THD testing remains as an excellent tool for circuit designers, manufacturing and maintenance. Because if anything goes amiss in a circuit, it will show up as an unexpected THD value.

 

[Ampdog]

Verdinut,

Yes, a figure at say 500 Hz or 1 KHz would be more meaningful, if that is all one is capable of measuring.

Distortion measurements are more meaningful if they could also include harmonic components separately instead of the sum of the total, because some products e.g 7th, 9th and 11th harmonics (yes, that high up!) can be so troublesome that even near the threshold of hearing they can cause 'stridency'. (Note that the culprits are mainly odd order harmonics. Even order ones are so many octaves higher, hardly disturbing in small quantities.) It refers a.o. to a phenomenon called listener's fatigue, about which you can read up om the internet.

Previous research created knowledge of how hearing reacts to such, which is then at present used to determine any possible problems. You can get very good info regarding this on the internet. The story can become involved, but experience helped to 'create' a model of hearing which one can then use to get pretty fair piture of how 'clean' an amplifier is. (Mercifully for us there are auditory limits of human hearing which is to our advantage.)

 

[MR.MAGOO]

I've got tinnitus so everything is distorted.

 

[Art Vandelay]

What's the use of testing for THD at 20 kHz on audio equipment when the 40 kHz harmonic, for instance, is way beyond the human range of hearing? We're not bats!

Even if the harmonics are out of band, low distortion @ 20kHz provides confidence that high frequency intermodulation distortion will also be low.

So it's definitely a useful metric.

 

[highfigh]

Not all distortion is harmonic and or linear. However the absence of THD at 20 KHz is pretty good evidence that things are A OK.

Just because the hearing limit is 20 KHz does not mean that trouble around 20 kHz is not audible. It certainly is at times. The most notable example I can think is aluminum dome tweeters. Even the best of them break up violently at 20 KHz or just above. You would think this would not be audible. However many including myself can hear it. It adds a peculiar sizzle to the reproduction that is not highly noticeable, but it is there and enough to put me off using them. Many have noted this.

The other thing is many early CD players had anti aliasing filters that did peculiar things around 20 KHz. This was definitely audible. In 1984 I expended significant funds to obtain a Revox player designed by Roger Lagadec that did not do this. Most early CD players had a problem here and got CD an early bad rap.

So yes, knowing there is good performance out to 20 KHz is a required benchmark.

IIRC, the problems with early CD players was more in the area of IM distortion, so the clash between the sampling rate and the "brick wall" filters produced enough distortion that the difference frequencies were clearly in the audible range until they started doubling what they called 'over-sampling'.

It was great hearing music without noise, but then, we had to listen to the sound of discs that hadn't been re-mastered for CD. Yeesh!

 

[M Code]

IIRC, the problems with early CD players was more in the area of IM distortion, so the clash between the sampling rate and the "brick wall" filters produced enough distortion that the difference frequencies were clearly in the audible range until they started doubling what they called 'over-sampling'.

It was great hearing music without noise, but then, we had to listen to the sound of discs that hadn't been re-mastered for CD. Yeesh!

Early CD players used (2) different chip sets, 1 was from Japan and 1 was from Europe. The chip set from Europe (Phillips) was much smoother with 4X oversampling and was very musical without alot of the mentioned audible artifacts. @ that time Philips had bought Marantz so their players used the Phillips chip set. Even today those Marantz CD players sound very, very good...

Just my $0.02...