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

 
Chris, i am studying the waveTable and OscillatorNode code.  i'm sorta assuming you're in the file's heritage, i dunno.
 
don't s'pose there's a pitch or period estimator in this, is there?
are you guys doing any analysis tools that would take a recorded
note and extract either additive synth data (that can be fed to createBandLimitedTables()  or the extractive wavetable directly from the pitch-tracked data?  
you might want the means to a more general wavetable definition than SINE, SQUARE, SAWTOOTH, and TRIANGLE.  it
might be hard to find some of it, it's very old (pre-1996), the computer that it lives on hasn't been turned on for a while, but i did this before, including what you did defining wavetables.  and i might be able to find some MATLAB code of the same vintage.
 
btw, i am curious
about the cos(0.5 * omega) factors in SAWTOOTH and TRIANGLE. (and not in SQUARE).  what is that factor for?
and i was looking for where CentsPerRange might be used.  that would be interesting code i presume building a "keymap" of ranges or whatever you call the set of
wavetables that correspond to different places on the keyboard.  in some semantics, a "wavetable" is an array of what we might be calling a wavetable here (which is an array of a single period of samples).
 
so you can have that array of wavetables with 2 or more
dimensions ("slow time", pitch, key velocity, key pressure, modwheel, pedal;  joystick, slider, i dunno whatever controller).  and you can interpolate in any or all of these dimensions, but it gets costly.  you double the number of linear-interpolations every time you add a
dimension to interpolate in.
 
r b-j
 

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

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

From: "Chris Rogers" <crogers@google.com>

Date: Thu, May 9, 2013 2:57 pm

To: "Ehsan Akhgari" <ehsan.akhgari@gmail.com>

Cc: rbj@audioimagination.com

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

--------------------------------------------------------------------------



> On Thu, May 9, 2013 at 7:26 AM, Ehsan Akhgari <ehsan.akhgari@gmail.com>wrote:

>

>> On Wed, May 8, 2013 at 11:54 PM, Chris Rogers <crogers@google.com> wrote:

>>

>>>

>>>

>>>

>>> On Wed, May 8, 2013 at 8:46 PM, <rbj@audioimagination.com> wrote:

>>>

>>>>

>>>>

>>>> it seems to me that if the createWaveTable() method is, essentially, an

>>>> inverse DFT. is it anything else?

>>>>

>>> That's the basic idea, but then this time-domain version has to be

>>> sampled at many different rates, so we want to avoid aliasing. In WebKit

>>> (Blink is the same) we use a multi-table approach (similar to mipmaps for

>>> graphics) where each table uses an inverse DFT, culling out an appropriate

>>> number of aliasing harmonics. Then when we render the waveform, we select

>>> which two adjacent tables to use, interpolate between those two, and then

>>> use linear interpolation...

>>>

>>> https://svn.webkit.org/repository/webkit/trunk/Source/WebCore/Modules/webaudio/WaveTable.cpp

>>>

>>> https://svn.webkit.org/repository/webkit/trunk/Source/WebCore/Modules/webaudio/OscillatorNode.cpp

>>>

>>> We have tests where we load up a WaveTable and use it with an

>>> OscillatorNode, sweeping the frequency from very low to high (something

>>> like 10Hz -> 20KHz), checking that the aliasing isn't too bad...

>>>

>>

>> That is my point. :-) It should be possible to implement WaveTable (and

>> OscillatorNode) without linking to the WebKit implementation!

>>

>

> But I think the spec is very detailed and quite clear on what the WaveTable

> and OscillatorNode should do mathematically. It doesn't dictate a specific

> technique for achieving the effect. I only mentioned the WebKit code here

> as one possible practical approach.

>

>

>

>>

>>

>> --

>> Ehsan

>> <http://ehsanakhgari.org/>

>>

>