Hi,
I can't tell you anything about the implementation details of
the VPIO unit, but we have recently implemented a simple word
recognition algorithm where we used the VPIO unit to record
speech samples. The recording quality of the VPIO was great for
speech and we have got a much cleaner speech signal than using
the RemoteIO.
Our project is available at GitHub. As far as I know there is
no sample code available from Apple using the VPIO unit. So you
might be interested to do a quick test with your recording
scenario using our SOVoiceRecorder class (you could just rip out
of the rest, it does not have any special dependencies to other
classes of the project):
It's really a very simple implementation with the only goal
of recording stuff into a CAF file. Use it like this:
SOVoiceRecorder * recorder = [[SOVoiceRecorder alloc] init];
[recorder startRecordingIntoFile:someFileURL];
//Recording...
[recorder stopRecording];
[recorder release];
Also, in line 191 of SOVoiceRecorder.m you could just
uncomment some code to disable AGR. If you want to compare the
VPIO recording to the standard RemoteIO recording, just
comment/uncomment the code surrounding line 129 of
SOVoiceRecorder.m appropriately. Since we were just recording
speech in our project, we have only used 16khz as the sample
rate. It should be easy to modify this accordingly (e.g. line
213, line 262).
Hope that's useful to you.
Let me know if you have any questions,
Heinrich
On Apr 26, 2011, at 18:16 , Zachary Kulis wrote:
Hi - does anyone know whether the VPIO AGC manipulates
the actual
microphone gain or simply scales the audio samples? I
would like to know
whether enabling the AGC via the
"kAUVoiceIOProperty_VoiceProcessingEnableAGC" property can
increase the
SNR of the recorded signal.
Thanks,
Zachary Kulis
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