How to fix a recording which have been sped up from the recorder using DPC?

[THpubs]

In my Sony recorder I accidentally switched on DPC speed control. I recorded for more than an hour (I can't remember exactly) but the output file is about 5 minutes. It sounds like a file which have been sped up. How can I undo this?

Here's a sample file : https://www.dropbox.com/s/xsqw7nn0tth01tx/dpc.mp3?dl=0

[THpubs]

When played from the recorder it works fine.

[Cornucopia]

You need to do a sample rate adjust (which is NOT the same thing as a sample rate conversion, because that resamples the clip). This will change the header that says the file is sampled at 44.1kHz down to something lower.

I did a quick trial in Audition, though you could use most decent audio editing apps including Audacity, and changed the SR from 44.1kHz down to 16kHz. 22.5kHz was too high, 11.25kHz was too low. Your actual best choice might be different. Strangely though, if this WERE the proper resultant SR, your 5 min. clip ought to only be ~13-14min., NOT an hour. Possibly this "DPC" thing may use variable speed? And if so, that would make adjustment MUCH more difficult & painstaking, where you'd have to have to work with adjusting individual segments at different rates before recombining them.

Here's the sample, with the header changed to 16kHz (and then resampled back to a normal 48kHz for common usage). I also chose only one (the stronger Left) channel of the 2 channel source clip, in order to minimize interference and provide a better resultant mono bitrate without going TOO large for an example.

Note, changing the header in this way exposes the fact that the device (probably) did not properly use an anti-aliasing filter on the lower sample rate (my guess is that it used a static HF filter without accommodating the temp lower sample rate which would require a Lower Freq filter to accompany it). As a result, you will hear "birdies" or "squiggles" in the final, corrected stream, and this is near impossible to reduce, much less eliminate.

Scott

BTW, your clip is so small, there was no need to use DropBox - you could have uploaded it directly here! For a full hour's worth, DB might be the better method, though. Also, it would help further testing/troubleshooting if you were to list the exact model # of your device.

[Brainiac]

I do not own one of these recorders, but in an attempt to help I read a bit of the manual. According to the manual (as I understood it), DPC is for playback only. If that is indeed the case, then can the OP just turn off DPC (as stated in the manual) to resume normal playback speed?

Brainiac

[THpubs]

You need to do a sample rate adjust (which is NOT the same thing as a sample rate conversion, because that resamples the clip). This will change the header that says the file is sampled at 44.1kHz down to something lower.

I did a quick trial in Audition, though you could use most decent audio editing apps including Audacity, and changed the SR from 44.1kHz down to 16kHz. 22.5kHz was too high, 11.25kHz was too low. Your actual best choice might be different. Strangely though, if this WERE the proper resultant SR, your 5 min. clip ought to only be ~13-14min., NOT an hour. Possibly this "DPC" thing may use variable speed? And if so, that would make adjustment MUCH more difficult & painstaking, where you'd have to have to work with adjusting individual segments at different rates before recombining them.

Here's the sample, with the header changed to 16kHz (and then resampled back to a normal 48kHz for common usage). I also chose only one (the stronger Left) channel of the 2 channel source clip, in order to minimize interference and provide a better resultant mono bitrate without going TOO large for an example.

Note, changing the header in this way exposes the fact that the device (probably) did not properly use an anti-aliasing filter on the lower sample rate (my guess is that it used a static HF filter without accommodating the temp lower sample rate which would require a Lower Freq filter to accompany it). As a result, you will hear "birdies" or "squiggles" in the final, corrected stream, and this is near impossible to reduce, much less eliminate.

Scott

BTW, your clip is so small, there was no need to use DropBox - you could have uploaded it directly here! For a full hour's worth, DB might be the better method, though. Also, it would help further testing/troubleshooting if you were to list the exact model # of your device.

Thanks a lot for your help! The sample you sent is perfect! I will try it tomorrow morning and let you know the result Very sorry I only uploaded a short portion of the file. Here's a new file with a short english recording (very short) https://www.dropbox.com/s/g20dlf4ebgl47y5/150702_004.mp3?dl=0 . But since you have a solution we might not need this

[THpubs]

I do not own one of these recorders, but in an attempt to help I read a bit of the manual. According to the manual (as I understood it), DPC is for playback only. If that is indeed the case, then can the OP just turn off DPC (as stated in the manual) to resume normal playback speed?

Brainiac

I think it might be a problem with that setting. If I turn it off and play from the recorder things are fine. But if I take it to the pc I face the problem!

[Cornucopia]

Thanks a lot for your help! The sample you sent is perfect! I will try it tomorrow morning and let you know the result Very sorry I only uploaded a short portion of the file. Here's a new file with a short english recording (very short) https://www.dropbox.com/s/g20dlf4ebgl47y5/150702_004.mp3?dl=0 . But since you have a solution we might not need this

Using the same technique, I got this...

It sounds SLIGHTLY sped up, so the SR should probably be 14kHz or 15kHz or something, not 16kHz.

Scott