Subject: Re: Granular synthesis and auditory segmentation From: at <meijerNATLAB.RESEARCH.PHILIPS.COM> Date: Wed, 14 Oct 1998 19:18:25 +0200Richard Fabbri wrote: > Does this set of facts make anyone wonder why we bother to sample > the WHOLE waveform and continue to apply Fourier transforms to these > Bipolar samples when Nature does Not ?! > > Nature has a much simpler solution in Time Domain! I don't know about your neurons, but mine completely fail to replenish their synapses above about 1 or 2 kHz even after plenty of coffee. Of course there is a role for non-Fourier type processing too, but no simple scheme covers the entire audible [20 Hz, 20 kHz] range. Didier Depireux clarified the issue very nicely: > The half-wave rectification occurs _after_ the frequency > decomposition performed on the basilar membrane, i.e. > after you have decomposed the signal into frequency > channels. For these and other reasons, I'm more interested in granular synthesis applications that operate up to say 5 or 6 kHz by taking into account this frequency decomposition performed on the basilar membrane. To me a relatively weak effect that breaks down above 1 or 2 kHz would appear of little use. In my experience, using a logarithmic frequency scale and linear time axis makes the "textural aspect" (i.e., the patterning) in sound textures perceptually relatively invariant to their position in the time-frequency plane with a typical [0s, 1s] by [500 Hz, 5 kHz] area. That is also what I would want, since it keeps the perceptual qualities of overall time-frequency "position" and sound "pattern" largely independent, just as in vision the texture of an object doesn't appear to change and interfere with position of that object in the visual field. Of course the "art" is to optimize this preservation of invariants in the cross-modal mapping, while maximizing resolution and ease of perception (including "proper" grouping and segregation, possibly by manipulating the sound textures). Best wishes, Peter Meijer The vOICe Learning Edition - Seeing with your Ears! http://ourworld.compuserve.com/homepages/Peter_Meijer/winvoice.htm Email to AUDITORY should now be sent to AUDITORY(at)lists.mcgill.ca LISTSERV commands should be sent to listserv(at)lists.mcgill.ca Information is available on the WEB at http://www.mcgill.ca/cc/listserv