Why does a lowpass increase file size?

Windows 10
Audacity 2.1.1

Yeah I know this is probably a stupid question.
But I’m not a big audio buff, I kind of just use stuff as I need it.

So here is what I’m doing.

I’m dumping Mega Drive / Genesis tracks via XMPlay, saving output as 24bit FLAC.
Then I open that in Audacity, throw a 4680Hz lowpass on it to help tone it down and get rid of some of the harshness / try to come close to a Model 1 unit.

Then I export it back out as 24-bit 44.1Khz FLAC.

Imported FLAC (Produced by XMplay/LibFLAC) file size for a particular track was 19,388KB
Exported FLAC (Produced by Audacity ) file size for lowpassed track was 32,069KB
Both used maximum compression setting.

I -could- get the file size back down by outputting it as 16-bit… But I don’t see why I should have to do that. Nor do I understand why the file size is increasing.
Maybe that’s just the way these things are, that’s cool too. I’m just curious to learn why, or if there may be a problem I need to correct with settings somewhere.

Also as an aside, the FLACs exported from Audacity identify as written by LibFLAC 1.0.4 - that can’t be right??
I just installed the latest updated to 2.1.1 to make sure as it mentioned updating to 1.3.1

It’s a bug - 1.3.1 is being used but the libFLAC version is written incorrectly in the exported file. It will be fixed for the next 2.1.2 release.


Such a Low Pass should reduce the exported file size a little. Perhaps your XMPlay file was really 16-bit.

You could use “MediaInfo” from http://mediainfo.sourceforge.net/en/Download/Windows to check the file. Get the version without installer, because the installer may have malware or adware.



You may be right… I am seeing something weird going on with XMplay. It doesn’t seem to respect output settings. However if you change the output bitrate and check with mediainfo it will show whatever value you selected. File size is practically the same though. It appears to be forcing 16-bit output for whatever reason.

Guess I’ll just output 16 from audacity then. Sounds pretty good either way :laughing: