I've been recording weekly 1 hour lectures, which uses up about 25-30Mb (I download the files to my laptop). Lately, the size has expanded to more than 90Mb, for the same one hour recording time. Any idea why?
If you open the recordings in Quicktime and open the inspector, it will show the data rate, sampling rate and whether it was recorded as mono or stereo. There could be variations other than the format such as if the mic was in a different location, it might have picked up sound from somewhere that it had to encode like more noise from the audience or something.
Thanks! Yes, now I see that the bigger files are in stereo, with about four times the data rate as the mono files. So now I've been trying to figure out why the files are in stereo - I didn't knowingly do anything different for these recordings. I haven't been able to find a place where there is a setting for this in Voice Memo, nor have I found anywhere online that explains this. Any thoughts? Thanks again!
Thanks! Yes, now I see that the bigger files are in stereo, with about four times the data rate as the mono files. So now I've been trying to figure out why the files are in stereo - I didn't knowingly do anything different for these recordings. I haven't been able to find a place where there is a setting for this in Voice Memo, nor have I found anywhere online that explains this. Any thoughts? Thanks again!
The internal iPhone mic records in mono but external mics can record in stereo. If you have an external mic, check if there's a switch to change between mono and stereo. Some mics have an on switch that has multiple positions for mono or stereo.
This was done just with the iPhone itself, no external mic's. That's why it's puzzling that the files came out as stereo (and idiosyncratically - sometimes mono, sometimes stereo, but always recording the same way). Is there even any way to set it to record in stereo format even though it's just the mono internal mic? Or could there be something I did accidentally that would make it think that it has an external mic? Or a noise level that would make it automatically switch to high quality mode?
The extra Mb won't threaten my life or anything, but I'm just so baffled...
This was done just with the iPhone itself, no external mic's. That's why it's puzzling that the files came out as stereo (and idiosyncratically - sometimes mono, sometimes stereo, but always recording the same way). Is there even any way to set it to record in stereo format even though it's just the mono internal mic? Or could there be something I did accidentally that would make it think that it has an external mic? Or a noise level that would make it automatically switch to high quality mode?
I don't think there's a UI setting to force it one way or the other. The newer iPhones have multiple mics but I wouldn't have expected it to randomly switch between stereo and mono, it uses them for noise cancellation:
One thing to check is if they are actually stereo audio files and not just dual mono, which is putting the same audio into each stereo channel. If you open the audio files in an app that shows the waveform like Audacity ( http://audacityteam.org ) or WavePad ( http://www.nch.com.au/wavepad/ ) and view both channels/waveforms side by side, you can check if they have unique patterns. You can test a recording by tapping the microphone locations individually so tap the bottom of the phone, top front, top back to see if the taps show up in separate channels. Try tapping all 3 in one recording and then just one in another and see if they come out differently. Maybe if it detects a difference in sound at one of the mics, it switches to stereo or rather HD Voice ( https://en.wikipedia.org/wiki/Wideband_audio ), which would explain the higher data rate.
Are you importing all the tracks to the Mac the same way i.e always taking them off the iPhone via iTunes or are some imported via email? There might be a conversion process happening with some methods of moving the files e.g stereo being downconverted to mono for email or changed from mono to dual mono.
The files were transferred the same way, via "TouchCopy12". I tried re-transferring, same result.
I also opened the files in Audacity, and the smaller files are mono, whereas the larger ones are stereo, and as far as I can tell the waveforms are identical.
If you have any further suggestions I'll be glad to hear/try them. Right now it looks like it has only happened with three files, so the problem seemingly has disappeared. For now I may have to settle for being mystified. In any event, thanks for your advice and sharing your knowledge - I really appreciate it.
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Thanks! Yes, now I see that the bigger files are in stereo, with about four times the data rate as the mono files. So now I've been trying to figure out why the files are in stereo - I didn't knowingly do anything different for these recordings. I haven't been able to find a place where there is a setting for this in Voice Memo, nor have I found anywhere online that explains this. Any thoughts? Thanks again!
The internal iPhone mic records in mono but external mics can record in stereo. If you have an external mic, check if there's a switch to change between mono and stereo. Some mics have an on switch that has multiple positions for mono or stereo.
This was done just with the iPhone itself, no external mic's. That's why it's puzzling that the files came out as stereo (and idiosyncratically - sometimes mono, sometimes stereo, but always recording the same way). Is there even any way to set it to record in stereo format even though it's just the mono internal mic? Or could there be something I did accidentally that would make it think that it has an external mic? Or a noise level that would make it automatically switch to high quality mode?
The extra Mb won't threaten my life or anything, but I'm just so baffled...
Thanks again!
I don't think there's a UI setting to force it one way or the other. The newer iPhones have multiple mics but I wouldn't have expected it to randomly switch between stereo and mono, it uses them for noise cancellation:
http://www.phonearena.com/news/Apple-iPhone-5-has-three-microphones-and-HD-voice-support-whats-in-it-for-you_id34486
One thing to check is if they are actually stereo audio files and not just dual mono, which is putting the same audio into each stereo channel. If you open the audio files in an app that shows the waveform like Audacity ( http://audacityteam.org ) or WavePad ( http://www.nch.com.au/wavepad/ ) and view both channels/waveforms side by side, you can check if they have unique patterns. You can test a recording by tapping the microphone locations individually so tap the bottom of the phone, top front, top back to see if the taps show up in separate channels. Try tapping all 3 in one recording and then just one in another and see if they come out differently. Maybe if it detects a difference in sound at one of the mics, it switches to stereo or rather HD Voice ( https://en.wikipedia.org/wiki/Wideband_audio ), which would explain the higher data rate.
Are you importing all the tracks to the Mac the same way i.e always taking them off the iPhone via iTunes or are some imported via email? There might be a conversion process happening with some methods of moving the files e.g stereo being downconverted to mono for email or changed from mono to dual mono.
The files were transferred the same way, via "TouchCopy12". I tried re-transferring, same result.
I also opened the files in Audacity, and the smaller files are mono, whereas the larger ones are stereo, and as far as I can tell the waveforms are identical.
If you have any further suggestions I'll be glad to hear/try them. Right now it looks like it has only happened with three files, so the problem seemingly has disappeared. For now I may have to settle for being mystified. In any event, thanks for your advice and sharing your knowledge - I really appreciate it.