[sdiy] saw vs ramp, audible?

[mskala at northcoastsynthesis.com]

On Tue, 10 Dec 2024, Roman Sowa via Synth-diy wrote:

> I regret to admit that I hear the difference too. One direction seems to have
> more lower end than the other. I thought maybe mp3 conversion messed up

It seems to me that in order to test this properly, one should have
objective evidence that the pressure waves really do have the same
power spectra for sawtooth and ramp.

If you use sawtooth/ramp electrical waveform -> speaker or headphones ->
ears and the two sound different, you don't know whether that is really
because the ears are responding differently, or the speaker or headphones
(and other things in the chain upstream of the ears) are causing a
difference in power spectrum and the ears are just detecting that.

Instead, one should do:  sawtooth/ramp electrical waveform -> speaker or
headphones -> microphone -> electrical waveform.  Verify that the power
spectrum is the same for sawtooth and ramp in *that* setup, and then you
can guess that a perceived difference is really being introduced by the
ears.

Of course this requires more pieces of good technology (in particular, the
mic) than just going one way, but it seems to be the only way of being
sure that the effect is really caused by the ears.

On the other hand, there does seem to be abundant other evidence, and
sound theoretical reason, to believe that identical power spectra do
sometimes sound different to human ears when they differ by phase.  Some
of the examples of identical power spectra in my article at:
   https://northcoastsynthesis.com/news/do-you-really-want-that-scope/
sound *almost* but not *absolutely* identical and it's reasonable to guess
that that's not only because of MP3 compression or nonlinearities in the
speakers etc.  I think one reason may be that the ears are doing envelope
detection - for instance in my "FM versus AM" example.

-- 
Matthew Skala
North Coast Synthesis Ltd.