Re: iPhone, iPad sampling rates
Re: iPhone, iPad sampling rates
- Subject: Re: iPhone, iPad sampling rates
- From: William Stewart <email@hidden>
- Date: Mon, 16 Aug 2010 18:31:42 -0700
So, we think it should work like this:
"if you are unmixable" then you get to have control of the audio hardware while you are active (not interrupted, so this is still the case if you are the current active app in the background).
This would behave like iPod playing in the background where it can change the hardware sample rate.
If you are interrupted while in the background, then you could decide to become "mixable" (as a non-mixable app you cannot re-activate yourself in the background), and just cooperate with the hardware settings as they are (because now an app with a more recent presence than yours is with the user)
So, while in the background, this workflow should work:
active - non-mixable
while you are in the background:
interrupted (as a non-mixable app is now in the foreground)
make your app mixable
make your app active
Bill
Begin forwarded message:
> From: Stéphane Beauchemin <email@hidden>
> Date: August 12, 2010 9:10:29 AM PDT
> To: Raphaël - Mancing Dolecules <email@hidden>
> Cc: email@hidden
> Subject: RE: iPhone, iPad sampling rates
>
> I have done some test with files at 32kHz and 48 kHz, and the MusicPlayer changes the device sampling rate depending on what’s playing. Which make sense since it is probably more efficient this way in terms of CPU cylces and power consumption.
>
> I don’t know what happens with 3rd party app on the top of that, I guess that the first app requesting sample rate for background audio gets it the second app has do to with it.
>
> From: email@hidden [mailto:email@hidden] On Behalf Of Raphaël - Mancing Dolecules
> Sent: August-11-10 7:10 PM
> To: Stéphane Beauchemin
> Cc: email@hidden
> Subject: Re: iPhone, iPad sampling rates
>
> Interesting note indeed.
>
> As third-party apps are now allowed to run audio in the background, thanks to iOS 4, I would bet that the behavior you noticed with the iPod app would be reproduced with some other "audio backgrounding" app. Possibly with different sample rate than 44.1 kHz, depending on, and if, they have setted their own kAudioSessionProperty_PreferredHardwareSampleRate.
>
> Pandora, Spotify or music creation apps like ThumbJam, which is very likely to use kAudioSessionProperty_PreferredHardwareSampleRate, could be used for testing this.
>
> Regarding the 44.1 kHz of the music player, if it can be something else, it would probably be the sampling rate of the played file itself. So feeding your iPod Touch with audio files with various sampling rates would be a good start point for testing, assuming there is no resampling/transcoding in the sync process.
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