"Phil" wrote in message news:3f221df9$0$20081


What is audible has been known for many years.

What level of THD is audible in your opinion then?


I use the term "THD" reluctantly, because that is what most people, in
this form, think of as *the* distortion test. Actually THD won't tell
if an amplifier or CD player, has audible distortion. THD will give
the level of the 2nd and 3rd harmonics, for various frequencies. That
is not enough information to predict the audiblity of distortion
generated by a complex waveform, such as music.

To predict audible distortion, we need to measure the level of beats
created by all possible combinations of tones.

Again, most of that kind of work was done years ago. The S/N
audibility studys that were done long ago (for tape and records) still
apply to the the audibility of noise on 24/192.

But ANY audible noise on 24/192 is obviously *NOT* due to limitations of the
format.
What are your figures? What is the required listening environment.


I'm not going to give figures. Do a Google Audio Group seach on:
'audibility noise'.

As testing methods get better, future listening tests will be required
to evaluate the new types of measurements.

Evaluation of amplifiers or CD players should be on the basis of
measurements, not listening tests. Measurements such as: frequency
response, phase shift, transient response, impulse response, group
delay, white noise, spurious noise (such as hum), jitter, 2nd order
intermodulation distortion, 3rd order intermodulation distortion,
crossmodulation distortion, transient intermodulation distortion,
overload recovery, clipping characteristics, and probably a couple
other things. Of course, after measurements have been done, a
listening test should be the final check.


Exactly, so what *ARE* you measuring that you believe will make a
difference?

I just started puting together the software and the hardware necessary
to perform a few, simple, measurments of audio distortion. I haven't
invented any new distortion measuring techniques. I'm just taking
existing techniques, and applying them to audio equipment. Look on
Arny's website and you will see he uses nonstandard (better) measuring
techniques.

Using measurments similar to Arny's, my first test was on the
computer's CD-player through an Audigy-2 sound card . The Audigy-2 sum
and difference beats measured more than 100 dB down (20 to 7000 Hz)!
My $49 CD player, on the other hand, has beats that measured of only
80 dB down. Listening to the two players, they sounded the same. Go
figure :-)

What new tests do I think will make a difference? I like the idea of
testing with forty simultainous tones, one at every 500 Hz, from 500
Hz to 20kHz, and measuring the amount of intermodulaton beat power
that lies "under" each tone. Until I acutally do this test, I will say
only that it looks promising.

Bob Stanton