MP3 files and sound quality

In which case I'd say you will get some losses over the original MP3 file. As to mix it with others means decoding and re-coding the final mix.

Thanks. On the subject of compression, the bulk of the files I'm working with are m4a recordings of a male speaking voice and they have a huge and impractical dynamic range. I was resigned to going through them (and there are a lot) manually adjusting the levels, but could applying compression achieve a decent quality result? I do need to retain the clarity and unmuddyness they have at present. I've very little experience with compression of audio files and would be grateful for any thoughts.

Thanks.

yes. that should work if you have a decent package. Audacity is not bad for that

Thanks. I do have Audacity, and the mixer program I'm using (MixPad) also has a built-in compressor. MixPad has a preset called "general voice level" which I suppose should be OK but Audacity requires manipulating a slightly daunting array of parameters. I suspect that this would give a better result if only I knew what settings would be best.

I've found a couple of tutorials on compression for spoken word audio which have given me some starting points. I'm getting quite a decent sound with these settings in Audacity:

Threshold -60 dB Noise floor -40 dB Ratio 3:1 Attack time 0.01 secs Release time 1 sec

I'll keep experimenting.

How long is a peice of string? Depends how wide a dynamic range you're having to deal with and what the loud bits are.

If the loud bits are coughs or laughs or shouting the chance are they can be controlled well enough with a limiter after a compressor.

If the "normal" speech has a dynamic range of 10 to 20 db a compressor set at 2:1 to 3:1 with around 6 dB of gain reduction happening ought to work reasonably well.

Just looked at Audacity's compressor/limiter "effects" and they aren't realtime. Being used to realtime, ie tweak and instantly hear/see the result, non-realtime totaly throws me.

Yes, I appreciate the point.

Mostly, Audacity shows the range as from -20 dB to -6 dB but there are occasional peaks of 0dB or above. All the files are of a man speaking, whispering, and sometimes shouting.

Sorry, I'm not sure what you mean by 6 dB of gain reduction. How does that relate to Audacity's parameters of threshold, noise floor, and ratio?

I can see how that would be useful. I suspect that realtime would need rather more processing power than I have available though. What software do you favour?

Dave, since my previous reply I've sussed out the Audacity compressor (it took me a shameful while to realise that the reduction was marked on the display's horizontal axis rather than the vertical one). I've been trying various settings and discovered that for the material I'm working with I need rather more than 6 dB reduction: 20 dB appears to be nearer the mark. That's if I want to retain a good contrast between the loudest and softest passages.

I'll keep experimenting.

Good one Bert. You have it sussed.

The Audacity compressor doesn't seem to work in the same way as the analogue one I have. So experimenting is the only way.

With pro analogue compressors, you could usually just enter your favourite settings for a given use, and expect it to be pretty well there.

Not really found a software one that acts in the same way.