RE: Setting a sample rate in the web audio API

---------- Forwarded message ----------
From: Grant Galitz <grantgalitz@gmail.com>
Date: Sat, Feb 12, 2011 at 7:28 PM
Subject: Re: Setting a sample rate in the web audio API
To: Chris Rogers <crogers@google.com>


I'd think that the buffer size in audioSource would not matter, because I do
drop it, but the rate at which my event handler for my onaudioprocess does
not sync up with the sample rate set for the audioSource's set sample rate,
but I believe it should. Even if I was ignoring the "input", the false input
should still be feed at the correct speed, of which the event handler is
obviously called at the wrong rate for refilling (timed against the
audioContext and not the false buffer I created, which seems wrong since I
connected the false buffer to the javascript node.).


On Sat, Feb 12, 2011 at 6:20 PM, Chris Rogers <crogers@google.com> wrote:

> Hi Grant,
>
> With this line:
> audioSource.buffer = audioContextHandle.createBuffer(1, 1, settings[14]); //Create
> a zero'd input buffer for the input to be valid.
>
>
> You're creating a buffer whose length is only 1 sample-frame (the second
> argument) which is pretty short!  And from what I understand, you're
> ignoring the "audioSource" input.  The sample-rate *is* taken into account
> in the "audioSource", it's just that you're ignoring what it's giving you
> and generating your own output stream.  The sample-rate of the AudioContext
> itself is fixed and is usually going to be the sample-rate of the audio
> hardware (such as 44.1KHz).
>
> Chris
>
> On Fri, Feb 11, 2011 at 12:41 PM, Grant Galitz <grantgalitz@gmail.com>wrote:
>
>> Hey, you probably already know my JS GameBoy Color emulator project
>> https://github.com/grantgalitz/GameBoy-Online
>> The thing is, I'm wondering why the web audio API refuses to allow me to
>> set my own sample rate (I want 70khz). Right now I have to set the sample
>> rate to that already found in the API itself:
>>  audioSource = audioContextHandle.createBufferSource(); //We need to
>> create a false input to get the chain started.
>>  audioSource.loop = false; //Keep this alive forever (Event handler will
>> know when to ouput.)
>>  settings[14] = audioContextHandle.sampleRate;
>>  audioSource.buffer = audioContextHandle.createBuffer(1, 1, settings[14
>> ]); //Create a zero'd input buffer for the input to be valid.
>>  audioNode = audioContextHandle.createJavaScriptNode(settings[18], 1, 2); //Create
>> 2 outputs and ignore the input buffer (Just copy buffer 1 over if mono)
>>  audioNode.onaudioprocess = audioOutputEvent; //Connect the audio
>> processing event to a handling function so we can manipulate output
>>  audioSource.connect(audioNode); //Send and chain the input to the audio
>> manipulation.
>>  audioNode.connect(audioContextHandle.destination); //Send and chain the
>> output of the audio manipulation to the system audio output.
>>  audioSource.noteOn(0);
>>
>> settings[14] being the sample rate 70000.
>> I need to do this to get it to work:
>> settings[14] = audioContextHandle.sampleRate;
>> Which effectively forces me to use the API's arbitrary sample rate instead
>> of one I want to use.
>>
>>
>