Re: [Audacity-devel] was: 'Re: Classic Filters status', now a little OT

[Federico M. <fm...@fc...>]

Martin,

> I believe nobody can, but it seems contested. If the phase changes 
> over a second or less, certainly the difference can be heard.

This is the sort of case discussed by Roederer.

> I can't hear it, can you?

Yes, I can hear some modulation.

> How did you get the 880.44 Hz? I'm interested to hear your analysis.

Sorry to disappoint you, it's very basic. I just looked at the waveform 
o rather the envelope and observed that it took about 2.5 s to complete 
sort of a cycle, then I generated a mistuned harmonic multiplyng by 
2.001 (which made a beat about that long with 2.000*f). The envelope is 
similar, not identical, but enough to test the idea. The same as in the 
case of frequency modulation, the spectrum of a very slight FM is very 
similar as the spectrum of an amplitude modulation (one tone and two 
side bands, with the only phase differences)

> Hmm. Can they really? 

I can't tell... Haven't run a double blind test. But more than once I 
have been surprised by people systematically hearing things I did not.

> I'm a bit sceptical, since as I've got older and better at listening, 
> my hearing has got worse. And are these 'experienced audiophiles' 
> lucky or not? is something I've often wondered. 'generally accepted' 
> references would be nice.

I don't have any at hand right now, but now and then I come across some 
comment of the like. I'll pay attention next time and send it to you.

>> But the subtle difference probably cannot be perceived at all in the 
>> presence of fan noise from the computer if not acoustically isolated. 
> Can you hear it?

I don't have an adequate environment. I don't believe even that I am the 
best subject to test these subtleties, since I have some tinnitus

>> A 1 kHz order 10 lowpass Chebyshev has at 1 kHz a phase delay of 
>> 720º, about 2 ms, while at 100 Hz it has a delay of 0.13 ms. That 
>> means that there is a difference of about 1.9 ms, which corresponds 
>> to a distance of about 2 ft, that's why the source may, in theory, 
>> seem blurred. 
> OK, it's a theory. Do you (or anybody else) have a procedure that I 
> can follow to demonstrate the difference in that delay and so (maybe) 
> be able to hear the problem? Something that we can do in Audacity by 
> generating waveforms, applying filters and so on? I'd love to try that 
> out on my young-eared students.

OK, I'll try to think of some test.

Regards,

Federico