Re: iPhone Sampling Rates
Re: iPhone Sampling Rates
- Subject: Re: iPhone Sampling Rates
- From: Jorn van Dijk <email@hidden>
- Date: Tue, 7 Jul 2009 10:45:16 +0200
Thanks for clarifying William,
So no option to have 8 kHz in and 44.1 kHz out on the 2G?
Jorn
On Jul 6, 2009, at 21:51 , William Stewart wrote:
On Jul 2, 2009, at 10:29 PM, Marcus Hobbs wrote:
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.
No, this has always been the case
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.
no
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*.
No
you are incorrectly determining the h/w sample rate. Have a look at
the AudioSession calls - these can be used to find out what the
hardware settings are (and make sure you audio session is active
before you make them, or you get state that is not necessarily
appropraite for your usage of the h/w)
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.
yep
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.
you would have been having software resampling done if the rate you
want is different than what you are using on the client side
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.
yes - but that was always the case.
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
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