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I am having a problem attempting to record from a Yamaha P-140 stage piano to Audacity 2.0.3 using a Roland Duo Capture USB audio interface. The recording comes out almost perfectly, apart from occasional tiny "pops" in the audio. Maybe 3 or 4 of these occur over a 2 minute recording. Zooming in on the offending section in Audacity shows that the wave is "broken", i.e. in both the left and right channels it jumps suddenly up or down and is not a smooth wave like the rest of the recording.

What I know so far:

  • I have a dual boot of Ubuntu 12.10 and Windows 7 and the effect is identical in both.
  • I have changed the sample rate on the Duo Capture from 44.1k to 48k with no effect.
  • I have changed the EXT option from * to ** on the Duo Capture with no effect (it must be on ** to be recognised at all in Ubuntu).
  • My laptop should be easily powerful enough to record without dropouts, the CPU usage goes no higher than 10% while recording. It has 6 GB of RAM. Therefore, I have not yet changed any quality settings in Audacity (apart from the sample rate to match the audio interface).
  • The Duo Capture is plugged into a USB 3.0 port.
  • I haven't yet tried any other recording software, but I've always read Audacity is quite highly rated.

I'm fairly sure the cause of this is not the piano, but I don't know whether it could be the audio interface, the laptop or the software. Any ideas at all?

(Later today I can upload a screenshot of the broken waveform if my description isn't clear enough)

Thank you!

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it is not uncommon for pops and skips to occur if there are hardware interrupts occurring. Additionally, because this is a laptop, you should try (temporarily) disabling power saving and dynamic CPU underclocking (aka SpeedStep; CoolNQuiet; probably in BIOS). Disk access is an order of magnitude slower than CPU and memory and Audacity may be flushing to disk periodically causing a pause. Run a resource monitor and sort the columns by cpu time and see if you can find a correlation with some process. –  horatio Jul 25 '13 at 21:18
    
Thanks for your comments so far everyone. I have placed a normal and slowed sample of the pop sound here: jkhemming.co.uk/upload/pop_sample.mp3 jkhemming.co.uk/upload/pop_sample_slow.mp3 –  Ozor Mox Jul 25 '13 at 23:26
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2 Answers

It would be helpful if you were able to post a sample of the audio, but the first thing that comes to mind, particularly if you are using an analog means of audio capture (1/4 inch cable for example), then it is quite possibly a problem with the cable or connectors. Sparks in the cable or at the connectors tend to be a common source of popping, but without a sample to listen to, it's impossible to identify for sure.

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I'll post a couple of samples this evening. I'll also try using something other than Audacity to record in case it makes any difference. –  Ozor Mox Jul 24 '13 at 14:01
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I got something like that due to a power supply issue. Very infrequent loud pops in the audio... turns out it was someone turning the lights on and off in the other room. A heater/AC unit can cause the same thing.

This was an odd case, and may not be your issue though.

For troubleshooting: You've got a laptop - so I'd try recording at another location first. You can try to isoloate the power using a uninterrupted power supply (UPS).

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Laptops come with built in uninterrupted power supply. Just unplug the laptop for perfect power isolation! –  ObscureRobot Feb 19 at 22:47
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