Re: [Bug 21980] New: WaveTable is highly underspecified

 
Joe, i'm still learning what the Web Audio API is about.  i am snooping at some of the files and, at present, the oscillatorNode and waveTable classes are getting my attention.
 
if this WebAudioAPI is meant to be only code for real-time synthesis and
processing, then this note analysis is in it.  but, in the waveTable.cpp code, i saw definitions for the wavetables for sine and bandlimited square, sawtooth, and triangle.  (BTW, i am convinced that the SQUARE is also off by a constant factor.)  all that is good for what it is. 
and there is code for wavetable playback that linearly interpolates (in one dimension) between two wavetables.  so there is the basis for coupling the timbre of the waveform to *some* control parameter.
 
i just think that constructing wavetable code that can interpolate in 2
or 3 dimensions efficiently would be useful.  it already appears that the pitch or MIDI key value is one dimension that is being considered.  but you need different sets of wavetables to make it useful, otherwise, we may as well leave it and what you'll have left are just bandlimited
oscillators.  but, wavetable synthesis is more than a means of doing non-aliased analog-like waveform oscillators.  that's what the note analysis would be good for.  but it should be an app (or a web app, i dunno) but it should produce wavetable data in a format that this Web Audio
API can take it and play it.  that's what i am suggesting.
 
Chris, the code comments say  "Copyright (C) 2012, Google Inc. All rights reserved." and "THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS..."  so exactly what rights are Google or
Apple reserving?  this is public domain, right?
 
also, Chris, the real-time synthesis code can be tightened up.  if you're willing to add one more sample at the end of the 4096-sample wavetable, so that waveform[4096]=waveform[0], then linear interpolation can be done
without having to do modulo arithmetic on the second point.  i found that to be a useful thing to do in the beginning.  wavetable synthesis can be done quite efficiently (compared to real-time additive synthesis) and you can "spend" some of the bandwidth saved by this efficiency
at interpolating in other dimensions for control and musical effect.  like a Prophet VS.  but the number of wavetables that are being mixed (using linear interpolation) is 2^num_dimensions.  if you have pitch (keyboard position), a slider or modwheel, and one other dimension to slide
around in (like slow time or something else), that's 8 simultaneous wavetables going and getting mixed just to get one note (but the phase accumulator and phase increment and modulo arithmetic and the mix parameters for between sample interpolation is the same for all 8).  so the core real-time
synthesis code should be the *most* efficient as possible.
 
r b-j
 
 

---------------------------- Original Message ----------------------------

Subject: Re: [Bug 21980] New: WaveTable is highly underspecified

From: "Joseph Berkovitz" <joe@noteflight.com>

Date: Sat, May 11, 2013 1:38 pm

To: rbj@audioimagination.com

Cc: "public-audio@w3.org" <public-audio@w3.org>

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> As useful as note analysis will be, my opinion is that it doesn't belong in the Web Audio API. It very much seems like something that belongs at the application level as there can be many implementations with different pros and cons and different degrees of user control over the process.

>

> &hellip;Joe

>

>> Chris, does this Java script code for note analysis exist somewhere? i don't know how to write Java or Java script, but what i have seen of Java looks a lot like C at the low level. if there is a place for this analysis code, i can do this in C and let someone else wrap it up in Java. it
requires pitch tracking, interpolation for the wavetable samples, and phase alignment of adjacent wavetables. the initial dumb version could have a wavetable for every millisecond or maybe every 2 ms. and, with a quick FFT on it, each extracted wavetable would have a line spectrum associated with
it, in case someone wants to knock off some harmonics (as well as for wavetable culling)
>>

>>

>> then we can discuss different ideas behind culling redundant wavetables. there are some issues there, particularly when interpolating along other dimensions. culling should happen only when the array of wavetables in *all* dimensions are being looked at. and adjacent wavetables should be
phase aligned in all dimensions, not just the slowtime dimension. that spinning of wavetables (to align them) should happen before culling. to within reasonable limits, there is not a time constraint on this analysis and wavetable extraction, because it is not real time. but you don't want to have
to take a long coffee break during the analysis either.
>>

>>

>> L8r,

>>

>>

>> r b-j

>>

>

>