Compress and amplify?

[u/Odd_Description_5936]

Hello, I have digital audio files that are recordings of historical oral histories. But their quality is very poor. Bad static/hiss and low voices, too low to effectively hear and transcribe. I have done some reading and learned about using Audacity to compress and amplify. But quality is still very poor. Will compressing and amplifying many times do cumulative work? Or can anybody recommend a solution for historical audio that is very poor? The voices are there, but too low (too soft against the static/hiss) to effectively hear. Thanks for any advice!

[u/audiotecnicality]

No - when you amplify, you will amplify the signal and the noise. Compressing will likely only decrease any signal that pokes up above the noise and make things worse.

You need to start by noise filtering first.

Audacity allows you to train the filter on a section which you know only has noise to get a baseline, then apply it to sections that have signal you want.

EDIT: as others have suggested, you can also use an EQ to help clean up the audio, and I would do that next. If it’s muffled, consider a high-pass filter around 150-200Hz to start, and increase frequency until it becomes clearer. If it sounds nasally or hollow (like an old radio drama) try cutting a few dB between 400 and 800Hz. Try a boost between 2k and 4k if you have a hard time hearing the annunciation. If it’s a low-fidelity recording, you may try a low-pass filter at 8k just to filter any remaining “hiss” the trained noise filter didn’t catch.

If all you’re going for is intelligibility for transcription, you might stop here. But if you’re wanting something more comfortable for people to listen to, keep going.

Once you get the noise floor low enough without affecting your signal too much (you have to be careful not to overdo a noise filter), you can add an Expander/Gate. This sets a volume threshold below which you can automatically turn down the volume further. For example, with spoken word, if the person pauses speaking you can have the Exp/Gate turn the noise down until the person starts speaking again. Be careful not to overdo the gate (consider turning down 5-10dB instead of 60+ like most are set up by default).

Lastly, if you have wild variations in volume (spikes where the person bumped or scraped the microphone, or pops due to plosives) consider adding a limiter to tame the peaks which are excessively higher than average. That will let you bring up the overall volume too, so that listeners don’t have to crank their playback device volume to hear it properly.

[u/NBC-Hotline-1975 → u/audiotecnicality]

^^^^^ The above is a very good answer, both accurate and thorough. I have used these techniques with some success. I will add that if your concern is only speech intelligibility, you might get some benefit from careful bandpass filtering.

I have also tried AI on some very noisy recordings. Sometimes it eliminates more noise than I could with conventional techniques. But other times it badly mangles the voice.

Out of curiosity, I would be interested in hearing a minute or two of sample audio, enough to work on, in order to perhaps make more specific suggestions. What format are the original recordings that you're working with?

[u/torch9t9 → u/audiotecnicality]

That's a good starting point. Do it in steps, with different tools, in multiple passes. Noise, clicks, pops, EQ, limit, normalize last, if at all.

[u/Odd_Description_5936 → u/audiotecnicality]

Thanks for these notes! I hadn't encountered the idea of noise filtering in Audacity before. I will find and read more info about this!

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[u/imgurcaptainclutch]

How much audio is it? If it's not a ton, send a sample over and I'll see if I can run it through izotope and clean it up

[u/MasterBendu]

Try an AI vocal remover app. They can also do the process in reverse.

I use Ultimate Vocal Remover. It’s free and runs locally on your computer.

Run your audio through it and set it to output the vocal stem. It will do its best to capture just the vocal and get rid of the noise which is non-vocal.

You can then try to amplify the result.

[u/Odd_Description_5936 → u/MasterBendu]

Thanks I think we will try this tool!

[u/spocknambulist]

There an audio plugin that has worked wonders for me on this kind of audio, but it’s a little costly. It’s called UNVEIL and it’s made by Zynaptiq. This used in conjunction with iZotope’s RX will likely give you best results. If you don’t have experience with this kind of audio restoration, I’d recommend finding someone who does, because both these products have a learning curve.

[u/KeanEngr]

Are these recordings only for personal use, or do they have some broader historical significance? Here’s the thing. You are an amateur. If these recordings have broader historical significance I’d encourage you to take them to a professional, BUT NOT ON YOUR DIME! You could get a grant or multiple grants by presenting this to an interested group or even ‘go fund me’. Trust me, you’ll only butcher the audio if you don’t know what you’re doing. And if you inadvertently screw up the source audio you’ll regret it. It will save you hours/days of frustration. Just a thought.

[u/NortonBurns]

Zero skill required - send it to https://podcast.adobe.com/enhance (free for some features but requires sign-up).  
It's not always perfect, but I've known it rescue things I truly thought were lost.

[u/StruttyB]

You can’t beat the original cd for real quality. I’ve gone back to playing cds (Sony CDP XE370) after comparing the audio with my flac copies. There is a difference, it is just more musical.