FLAC conversion in 16 bit should be improved

Audacity Help Forum Windows
1

Hi,

I’ve just discovered that the 16 bit FLAC conversion of Audacity could be greatly improved.

I have 24 bit FLAC files. As 24 bit is useless for listening purposes, I want to convert them to 16 bit FLAC files, and as it is a lossless format, it should sound the same. Well, first, I imported a 24 bit FLAC file into Audacity. Then “Export audio…”, select FLAC, level 8 (highest) and 16 bit.

Then, I imported into Audacity the resulting 16 bit FLAC, and compared it with the original 24 bit FLAC. Of course, if you listened to the tracks, both sounded the same. But I wanted to check if there had been a quality loss in the exported file. So I amplified the very beginning of the song 40dB, and there was noise there that shouldn’t be there.

So today I’ve just downloaded Foobar2000, installed the latest official FLAC enconder 1.3.1 x64 and converted the same 24 bit FLAC file to 16 bit FLAC. And this is the result, after amplifying 40dB the beginning:

PD: if you choose in Audacity to export to 24 bit FLAC, there’s no extra noise at all. Something’s wrong with the 16 bit conversion.

2

Did you read http://manual.audacityteam.org/o/man/faq_playback.html#dither?

Gale

3

LOL. Thanks! :laughing:

Anyway, why then when selecting 24 bit instead of 16 bit in the FLAC options window, there’s no dither at all?

4

What version of Audacity are you using? I would actually expect there would be dither on 24 bit FLAC exported to 24-bit FLAC. There should not be dither added, because if you are not downconverting the bit depth there is no need for dither, but we have Bug 22 – Exporting from integer internal formats to files in same format or higher adds unwanted dither noise.

Also be aware that Audacity does all processing in 32-bit float (even if the track is 16-bit or 24-bit), and that the 32-bit processed audio is then downconverted to the track rate if the track is 16-bit or 24-bit. So if you generate silence at 24-bit depth, then apply an effect like Fade In to the silence, the silence becomes dither noise. You can check that by looking at Effect > Amplify… before and after the Fade In.

Gale

5

I’m using of course the latest 2.1.0 version of Audacity. The 24 bit conversion is great, it has no noise, just like the original 24 bit FLAC I’m exporting.

6

Unless you turn dither off, both 16-bit and 24-bit FLAC exports have dither noise. The difference that you are noticing is that 24-bit dither has a much lower level (around -130 dB rms) compared with 16-bit dither (around -80 dB rms).

If you want “perfect” export with no dither OR quantize noise, export in 32-bit float WAV format.
If you want “perfect” export with no dither OR quantize noise, and you have not processed the audio in any way, then you can temporarily turn off dither in Preferences.

7

Lol, the thing is I’m starting out of a 24 bit FLAC file. And I want to size it down cause it’s so big and I only want it for listening purposes, so 24 bit is less than useless. So I want to convert it to 16 bit FLAC. I know how to do it, using Foobar2000 + official FLAC encoder 1.3.1 x64 gives you the perfect result I showed you in the first picture. May be if I turn off the dither of Audacity it gives me the same result as Foobar2000. But it’s solved right now.

I just thought it was Audacity’s fault that added some unwanted noise when exporting to 16 bit FLAC. Now I know it’s just the dither.

Thanks!