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How can I remove hiss in a recording (due to too-low level preamp)?

This was a live recording that I took from the mixing board on a Tascam, at 24-bit 96kHz recording. It has the direct input from the keyboard and the mics from the bass already mixed down to one stereo track.

Although it worked fine in rehearsal a few hours earlier, the keyboard came though at a very low level for reasons that were never determined (the plugs etc. were checked between numbers!)

So, the sound board operator had no choice but to crank the input up on the keyboard. This produced a noticeable hiss. Furthermore, he did a good job of ducking the level when he wasn’t playing, so the hiss comes and goes and changes volume all over the place.

The sample file is representative: you can hear how the hiss starts out loud and fades out when the other instrument (only) is playing.

I’m using Adobe Creative Suite, so what might I do in Audition to improve this?

(Note: I also have a recording made using a stand-alone Zoom recorder, in case that proves useful. I presume the direct recording is better for the clean-up though, as the recording of the speakers playing the hiss with natural room reverb added would be even more complex.)

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Michael Hansen Buur pretty much answered this question in his comment, or at least gave a shove in the right direction.

But having the tools is only a small part of successful noise removal. There are many different ways a noisy recording can be improved and only knowledge, practice and experience can tell you which to use and how to use it effectively.
But there is a limit to what noise reduction/audio restoration techniques can achieve. If the recording is important enough, and you can't get the result you want, it might be better to let a professional handle it, so you don't lose anything from the performance.

If you don't want to fork out for a professional job and want to DIY it, Adobe Audition does have a native noise reduction effect, which might work for your situation.

The ducking(noise gating) has worked against you here, it would be a lot better if the noise was continuous, so you could then get a noise print and strip it from the whole recording equally. There are many online tutorials showing how to use Audition's NR effect. But be aware of a few things;

  • The thing that will help you the most is a well timed noise gate(more precise than the live gating present in the recording, which also cuts off some release).
  • Overdoing the noise reduction can lead to watery artifacts, which can sound ten times worse than the original noise.
  • Even subtle noise reduction is better than noticeably losing frequency bands from the audio or losing meaningful transients. Practice should help you find the right balance.
  • Frequently switching between the original and the processed audio will help you to notice improvements and will stop you from getting tunnel vision and spoiling the performance. It will help you keep the original performance front and centre.

Keep these things in mind and with some practice and patience, you should get a result you are happy with.

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