USB audio interface recording levels

I’m using a Numark Stereo iO audio interface to convert some vinyl to digital. Its a phono turntable connected directly to the USB interface then to my computer. I am happy with the recorded sound but I’d like to tweak the input levels of the recording every so slightly in order to avoid clipping and depending on the sounds levels of the actual vinyl. The hardware has no volume/gain so I need do it via the software but I can’t figure out how to do it Audacity.

Any help would be gratefully received.

Audacity 2.0.3
Mac 0S X 10.7.5

You cannot on Mac. Apple don’t normally allow USB input devices to have a system input control, so there is no slider for Audacity to control. You can look in Apple System Preferences: Sound but it will probably say “The selected device has no input controls”.

If the input is clipped, a software control would only make the clipping quieter, not prevent it.

The Numark interface seems to have RCA outs you can get an adaptor to connect those to the Mac audio in, then you can control the input level coming into Audacity both through the volume control on the interface and the system/Audacity slider for audio in.


Many thanks for the extremely informative response, now I know exactly where I stand with regards to my setup. Brilliant.

I’m trying to adjust the recording input levels within Audacity 2.03 downloaded off the zip file on OS X 10.6.8 with a Sony PS-LX300USB turntable. The input slider in the mixer toolbar is greyed out though and I can’t seem to find a way of adjusting within Audio Midi Setup. From the comments I’ve read here, it looks like this is something I am not going to be able to change? Could you please confirm. I’ve got output through the computer speakers ok.

According to its Manual your turntable has RCA cables so you can adopt the same solution as was suggested to the original poster.

  1. Buy a stereo RCA to stereo 1/8 inch TRS adaptor.
  2. Set the turntable phono/line switch to line (see its manual, above).
  3. Connect the turntable’s RCA cables to the adaptor.
  4. Connect the adaptor to the Mac audio input.
  5. Set Audacity to record from the Mac audio input.

Now you should be able to adjust the input level in Audacity.


Thanks Gale, I’ll give that a try. Sounds like it will do the trick though. Thanks very much!