Re: iPhone Sampling Rates

Subject: Re: iPhone Sampling Rates
From: Marcus Hobbs <email@hidden>
Date: Thu, 02 Jul 2009 22:29:19 -0700
Delivered-to: email@hidden
Delivered-to: email@hidden

Hi Jorn and William,

I use the remoteIO unit for real-time voice processing in my iPhone app "SmackTalk!". I released the first versions of my app under OS 2.2.1. Under this OS, the hardware sample rate was always 44100 for all devices, and I assumed that it would always be so forevermore :-).

For the iPhone 2G this new behavior you describe was introduced during the 3.0 betas. Rumor has it that prior to 3.0 the default behavior was that some internal OS process "upsampled" the 8kHz mic to 44.1kHz so that the resulting hardwareSampleRate was always 44100. I never could discern the true history from the forums, but I know from experience that under OS 2.2.1 the 2G's hardwareSampleRate was always 44100, and under OS 3.0b5 and OS 3.0GS the 2G's hardwareSampleRate is now 8000 for the built-in mic *and 44100 for the external mic*.

With the advent of 3.0 for my application "SmackTalk!" I had to become more careful (like I should have in the first place!). Now I set the audio session properties and then check for the hardware sampling rate, instead of assuming that it will always be 44100. Your audio engine will now have to deal with very different sample rates. For my app, I include bundled samples and I have to provide different sample rates for the samples based on the resulting hardware sample rate. My app's character animation is driven by the sample rate, and so folks with a 2G have a different experience under 3.0 than they did under 2.2.1.

The new default behavior introduces subtleties I did not expect--what should I do if the user records files using the external microphone, AND records files with the built-in microphone? The new default behavior is such that a casual user could easily record files with different sample rates, whereas before the user could never do that. Every developer will have to answer this question in the context of their own app.

I released a fix for this three weeks ago, and it is still not approved, so I am constantly dealing with support emails and bad reviews. Once the new version goes on sale all will be calm. Hey-- what's this? I just got an email that OS3.1beta is ready for testing. Ah..the life of an app developer!

Marcus


On Jul 2, 2009, at 8:24 PM, William Stewart wrote:

nope
input is only 8K on the original phone
On Jun 29, 2009, at 3:14 AM, Jorn van Dijk wrote:
Hello there,
I'm pretty new to iPhone audio programming but I'm getting there. I'm using an AUGraph with a mixer and the remoteIO unit. I use the mic input to do some analyzing and then playback audio via the mixer through the remoteIO. When you enable the microphone on the iPhone2G the sampling rate switches to 8000 Hz. The iPhone 3G stays at 44100 Hz.

Does anybody know if it is possible to have the playback at 44100 Hz while the input is at 8000 Hz on the iPhone2G? This means that the remoteIO unit should have the input at 8000 Hz and the output at 44100 Hz.
What would be the way to connect them?
Thanks for any pointers.
Jorn _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: @apple.com

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Re: iPhone Sampling Rates
From: William Stewart <email@hidden>


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  >Re: iPhone Sampling Rates (From: William Stewart <email@hidden>)




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References:
	>Re: iPhone Sampling Rates (From: William Stewart <email@hidden>)