Removing hum and hiss

I’ve got a few CDs worth of amateur recorded small choir group, but there is a background hum and a lot of hiss. I’ve tried using the noise removal plugin but I can’t get anywhere near satisfaction without losing some clarity or getting a ‘reverb’ effect. Basically I don’t know what I’m doing. If I attach a sample of a track here (20 secs), can anybody have a go and see how good they can get it, then tell me how they did it please?

Windows 7 Pro, Audacity 2.0.1 from installer

Many thanks,

You won’t be able to make a huge improvement.
Here’s a (quickly done) idea of what to expect:

If you use the original recording rather than an MP3 version you may be able to get it a little better.

Before you start, Normalize (Effect menu) with all of the options enabled, to -1 dB.

If you use “Plot Spectrum” (Analyze menu) on the noise at the beginning you will notice two large spikes, one at 147 Hz and one at about 465 Hz. You can remove these with the Notch filter (Effect menu). Apply the Notch filter to the entire recording twice, once with each of those frequencies - try a Q factor of around 10.

Analyze the noise again. You will notice a narrower peak at 440 Hz. Apply the notch filter at 440 Hz with a Q or 20.
Repeat the process for the spikes at 100 Hz and 300 Hz.

Use the High pass filter with a frequency of around 100 Hz, 48 dB/Octave to remove the low frequency rumble.

Get a Noise profile with the Noise Removal effect, then apply the Noise removal effect to the entire track. The settings I used were:

Many thanks Steve - I think I’ve learnt a lot from just that single post. Would you mind if I continued this thread into the next stage of making the recording sound right?

I’ve pretty much followed your instructions with slightly different values because I was working from my original (which is still probably just a wavified mp3). I’m at the stage where I’m happy I’m not going to get any more noise reduction without losing sound clarity.

If you have a listen, you’ll notice a few things:

a) It has some distortion even though nothing is loud enough. I’ve looked for the offending (square-top?) wave patterns but can’t find any. What should I be looking for to detect them… I know I can draw them in correctly, but only if I know what the wrong ones are.

b) The tone is sort of tinny/think/overbearing (I don’t really know how to describe it). Is there any way of making it sound less ‘solid’?

c) I had a look at the equalizer, but it’s way way complicated - I was thinking I could use it to try and get a warmer sound.

I suppose, what I’m looking for is a step-by-step, “this is how to clean up this rubbish recording” guide. It’s quite important to me as these are early recordings of my choir which I’m trying to put on a CD in decent quality for posterity.

So far, I have:-

  1. Notch filter to get rid of regular unwanted tones
  2. High pass filter to get rid of low frequencies
  3. Noise removal

What could be next and in which order, using this rubbish recording as an example?

Many thanks,

Have you followed my trick?

Copy two secs of the file, press noise removal, get noise profile, press CtrlA to copy the whole lot, press noise removal, now before you press remove, set frequency to the maximum.

Setting the “frequency smoothing” to the maximum is not always the optimal setting. There is a trade-off between bubbly metallic artefacts if the frequency smoothing is too low, with loss of bass if set too high. The optimal position varies depending on the noise and the audio material, so it is worth experimenting.

The Noise removal effect is documented in the manual here:
and there is a tutorial that includes additional techniques here:

Try applying the Equalization effect with the 1000 Hz slider pulled down to about 1/4 (Graphic EQ view). That will help to tame some of the over-emphasis in that frequency range. Distortion is permanent - there’s not much you can do about that without causing additional damage.

True; but it’s just hissing, like on a cassette then it works. Pops from vinyl using click removal. I’m getting AAAwave as an alternative next month.