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

[Martyn S. <mar...@gm...>]

Hiya

On 03/01/2015 08:13, Federico Miyara wrote:
>
> Martyn,
>
>> Incidentally, can you hear the differences in these (440Hz and 880Hz
>> tones), I can't. https://dl.dropboxusercontent.com/u/1327769/phases.wav
>
> Except for the last one, nobody can, according to Ohm's law for mono
> signals (you cannot hear any phase difference):
>
> http://en.wikipedia.org/wiki/Ohm%27s_acoustic_law

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

> In the last one, if you listen attentively, you will notice a second
> order effect that is explained in the book by Roederer, "The Physics and
> Psychophyisics of Music". It is a case where the second harmonic is not
> exactly in tune. The phase modulation is similar either to frequency
> modulation or a mistuned second harmonic, for instance 440 Hz and 880.44 Hz.

I can't hear it, can you?

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

> As regards phase differences that depart from linear phase with
> frequency, it is generally accepted that they can be noted in stereo
> signals since they represent different delays for different frequencies.
> This affects the sharpness of the stereo image. Probably most people
> cannot tell the difference, but experienced audiophiles can.

Hmm.  Can they really?  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.

> 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?

> In the case of the antialiasing filters used in legacy A/D converters,
> I'm not sure if the audibility of this phase problem is not really due
> to the channel mismatch.
>
> 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.

Thanks
Martyn

> Regards,
>
> Federico
>
>
>
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