Re: Changing the sample rate of the audio device

> Pierre-Louis Bossart <mailto:pierre-louis.bossart@linux.intel.com>
> 11March 2013 5:42 PM
>>     Is there anything I can do about this in an application using Web
>>     Audio API? Is there a way to detect the changed settings? Or is it
>>     just a deficiency in WebKit?
>
>> This is really something to be handled at the user-agent level.  For
>> example, if an <audio> element is playing under the same circumstances
>> then it would be expected to adapt to the new hardware sample-rate.  So
>> ideally we'd like to have the AudioContext continue playing, adapting to
>> the new hardware internally.  I think it would be best in these types of
>> cases for the AudioContext to continue to operate at the sample-rate it
>> was created with, and that the user-agent simply does the appropriate
>> sample-rate conversion.
>
> Is there really a consensus on this?
> When changing accessories, both sampling rate and max number of 
> channels can change. If the sampling rate change is handled 
> internally, would the change in # of channels be hidden as well? 
> Changing channels mostly has an impact on virtualization and 3D 
> positioning, you wouldn't use the same settings and algorithms when 
> switching from headset to speakers.
> -Pierre

I would tend to disagree with the suggestion. I can reproduce the 
problem with an external DAC with a 96Khz sample rate. The very idea of 
having external decoder (whether it's a DAC or a home cinema or 
whatever) is to get a better decoding and rendering of the audio file 
being played. If we ask the browser to upsample from 44.1 whatever we 
can get as an output, it would be a huge loss in quality. Unless we 
reverse the paradigm and work at 96 all the time and downscale to the 
actual value of the existing hardware... which means more cpu usage.
IMHO the ideal way would be to get a notification from the browser of 
the decoder capabilities so that the code can be adapted accordingly. 
Plus, as Pierre mentions, in addition to raw sample rate, there are many 
others settings from a digital converter that are worth knowing.


Best regards
JC Verdié

>
>
> Chris Rogers <mailto:crogers@google.com>
> 6March 2013 10:22 PM
>
>
>     Hello,
>
>     when I run the following code and then change the audio output
>     device to a device with a different sample rate the sound is
>     distorted.
>
>     var context = new webkitAudioContext();
>     var gain = context.createGainNode();
>     gain.gain.value = 0.05;
>     var osc = context.createOscillator();
>     osc.type = 0;
>     osc.frequency.value = 440;
>     osc.connect(gain);
>     gain.connect(context.destination);
>     osc.noteOn(0);
>
>     http://jsfiddle.net/cQswX/1/
>
>     Even if I create a new context in the same tab after I changed the
>     output device the sound is still distorted. Only after I opened a
>     new tab (in Chrome) Web Audio API seems to adapt to the new settings.
>
>     I noticed this behavior when I plugged in head phones to my
>     notebook which is connected to a Cinema Display. The display audio
>     device has a sample rate of 48 kHz. The internal device has 44.1
>     kHz. The display was the initial output device. When I plugged in
>     the head phone the output switched to the internal audio device.
>     When I started playback the audio was distorted.
>
>     Is there anything I can do about this in an application using Web
>     Audio API? Is there a way to detect the changed settings? Or is it
>     just a deficiency in WebKit?
>
>     Best regards
>
>     Jan
>
>
> This is really something to be handled at the user-agent level.  For 
> example, if an <audio> element is playing under the same circumstances 
> then it would be expected to adapt to the new hardware sample-rate. 
>  So ideally we'd like to have the AudioContext continue playing, 
> adapting to the new hardware internally.  I think it would be best in 
> these types of cases for the AudioContext to continue to operate at 
> the sample-rate it was created with, and that the user-agent simply 
> does the appropriate sample-rate conversion.
>
> Chrome doesn't do anything fancy yet to adapt as I describe, so that's 
> probably why you were experiencing problems...
>
> Chris
>
> Jan Deinhard <mailto:jan.deinhard@gmail.com>
> 6March 2013 10:32 AM
> Hello,
>
> when I run the following code and then change the audio output device 
> to a device with a different sample rate the sound is distorted.
>
> var context = new webkitAudioContext();
> var gain = context.createGainNode();
> gain.gain.value = 0.05;
> var osc = context.createOscillator();
> osc.type = 0;
> osc.frequency.value = 440;
> osc.connect(gain);
> gain.connect(context.destination);
> osc.noteOn(0);
>
> http://jsfiddle.net/cQswX/1/
>
> Even if I create a new context in the same tab after I changed the 
> output device the sound is still distorted. Only after I opened a new 
> tab (in Chrome) Web Audio API seems to adapt to the new settings.
>
> I noticed this behavior when I plugged in head phones to my notebook 
> which is connected to a Cinema Display. The display audio device has a 
> sample rate of 48 kHz. The internal device has 44.1 kHz. The display 
> was the initial output device. When I plugged in the head phone the 
> output switched to the internal audio device. When I started playback 
> the audio was distorted.
>
> Is there anything I can do about this in an application using Web 
> Audio API? Is there a way to detect the changed settings? Or is it 
> just a deficiency in WebKit?
>
> Best regards
>
> Jan
> ------------------------------------------------------------------------