recording at 32float/96, does it dither on export to 24bit?

[bomber1978]

Hey,
I'm recording some internet radio, I set it myself to record at a sample rate of 96000, and the default is 32float, on export I select 24bit FLAC / 96000.
Does the 32bit float recording use dither when exported at 24bit?, I'm unsure if this is actually a sample rate 'conversion'.
Thanks
PS - I should add, that all I'm doing is recording the internet stream then exporting, no editing...

[Gale Andrews]

I'm recording some internet radio, I set it myself to record at a sample rate of 96000, and the default is 32float, on export I select 24bit FLAC / 96000.
Does the 32bit float recording use dither when exported at 24bit?, I'm unsure if this is actually a sample rate 'conversion'.

It's not a sample rate conversion but a bit depth conversion.

Yes the export will be dithered by default because the bit depth is being reduced. You could turn the dither off for the export in Quality Preferences (under "High-quality conversion") but the file should properly be dithered.

An alternative would be to set Quality Preferences to 24-bit Default Sample Format, then even if dither is enabled in Quality Preferences there will be no dithering if you don't run effects after recording and export to a 24-bit format.


Gale

[bomber1978]

I'm recording some internet radio, I set it myself to record at a sample rate of 96000, and the default is 32float, on export I select 24bit FLAC / 96000.
Does the 32bit float recording use dither when exported at 24bit?, I'm unsure if this is actually a sample rate 'conversion'.

It's not a sample rate conversion but a bit depth conversion.

Yes the export will be dithered by default because the bit depth is being reduced. You could turn the dither off for the export in Quality Preferences (under "High-quality conversion") but the file should properly be dithered.

An alternative would be to set Quality Preferences to 24-bit Default Sample Format, then even if dither is enabled in Quality Preferences there will be no dithering if you don't run effects after recording and export to a 24-bit format.


Gale

Sorry that was an accident, didn't mean to write sample rate, I meant bit depth but you knew what I meant anyway!...
Thanks will change that default to 24bit for this recording.
Thanks

[bomber1978]

If I want to "normalize" my 24bit recording (set at 24bit default) will this dither?
I don't think it needs dither?
Thanks

[DVDdoug]

If I want to "normalize" my 24bit recording (set at 24bit default) will this dither?

I don't know... You are changing the audio data, but the Audacity Wiki says:

An example of downsampling when converting a file is when you export from a 32-bit float or 24-bit project to a 16-bit export format.

So that's only when you export to 16-bit.

I don't think it needs dither?

I don't think so either... I wouldn't worry about it one way or the other... You can't hear 16-bit dither (around -90 dB) under any normal-reasonable listening conditions and you are NEVER going to hear dither (or the effects of dither) at 24-bits (around -140dB).

PS - I should add, that all I'm doing is recording the internet stream then exporting, no editing...

You might be worried about the wrong things... What's the quality (or bitrate) of the streaming audio? Whats the source of the original audio? Usually, streaming audio uses lossy compression, and the source material is likely "CD quality" at best, so there's probably no need for this high definition stuff.

[Gale Andrews]

If I want to "normalize" my 24bit recording (set at 24bit default) will this dither?

Yes, any Normalize operation will add dither noise because the audio is being processed at 32-bit float then downconverted to return to the track at 24-bit. Any process that recalculates the amplitude values of the samples will apply dither unless the track is at 32-bit float.

Audacity's dither is louder than the floor of the dB range. 24-bit shaped dither is at about-92 dB and 16-bit shaped dither is at about -73 dB.


Gale

[bomber1978]

You might be worried about the wrong things... What's the quality (or bitrate) of the streaming audio? Whats the source of the original audio? Usually, streaming audio uses lossy compression, and the source material is likely "CD quality" at best, so there's probably no need for this high definition stuff.

Yeah I know it's most probably not necessary to record an internet stream at 24/96, although it does sound pretty high quality, better than the FM broadcasts I have from cassette tapes of the same show! hah I plan to keep a hard copy on a DVD as DVD-Audio so I'm just going to keep it as 24/96.

[bomber1978]

If I want to "normalize" my 24bit recording (set at 24bit default) will this dither?

Yes, any Normalize operation will add dither noise because the audio is being processed at 32-bit float then downconverted to return to the track at 24-bit. Any process that recalculates the amplitude values of the samples will apply dither unless the track is at 32-bit float.

Audacity's dither is louder than the floor of the dB range. 24-bit shaped dither is at about-92 dB and 16-bit shaped dither is at about -73 dB.


Gale

In Preferences>Quality I have Default Sample Format set to 24bit, because I recorded an internet stream at 24bit and didn't need to dither as I didn't edit it, I just wanted the original recording kept...
So as I have Preferences>Quality set to a Default Sample Format of 24bit does that mean if I load in the 24bit file to Normalize it that it will still process at 32bit?, I thought having Default Sample Format set to 24bit would stop it processing at 32bit, this is why I asked the question, as I thought my 24bit file would be processed at 24bit (seeing as I have Preferences>Quality>Default Sample Format set to 24bit), so I thought a 24bit file being processed (normalized) at 24bit would not dither?, as I thought it only needs to dither when downconverting.... I guess I'm not totally understanding something here....?

[steve]

In Preferences>Quality I have Default Sample Format set to 24bit, because I recorded an internet stream at 24bit and didn't need to dither as I didn't edit it, I just wanted the original recording kept...

I'm not sure what happens if you used the new "WASAPI loopback" for recording, but if you recorded using "Stereo Mix" the digital stream is converted to analogue by your sound card, then converted back to digital and sent on to the recording program ("Audacity" in this case).

Where possible, best quality is achieved by downloading the audio rather than recording it. There are plug-ins available for Firefox that allow downloading of many (but not all) Internet audio streams.

I thought my 24bit file would be processed at 24bit (seeing as I have Preferences>Quality>Default Sample Format set to 24bit)

Processing within Audacity is always performed in 32 bit float format - in other words, Audacity performs calculations as accurately as possible.
An unfortunate side effect of this (imho this is a bug), if the track format is 16 or 24 bit, then by default, the audio is reconverted back to 16 or 24 bit (with dither is applied) after each process. Thus applying multiple processes to a 16 or 24 bit track will accumulate compound calculation errors.

When processing audio, highest quality is achieved by setting the "Quality" to 32 bit float format (default).

Compared to the losses involved with MP3 encoding, 24 bit dither is totally insignificant. As Gale and DVDdoug commented, shaped dither has a very low peak amplitude (around -120 dB peak), though it will sound even quieter. Low level noise is usually measured as "A-weighted rms". Audacity's "shaped" dither measures at around -138.6 dB A-weighted, which is very very very very quiet.

[bomber1978]

I'm not sure what happens if you used the new "WASAPI loopback" for recording, but if you recorded using "Stereo Mix" the digital stream is converted to analogue by your sound card, then converted back to digital and sent on to the recording program ("Audacity" in this case).

Where possible, best quality is achieved by downloading the audio rather than recording it. There are plug-ins available for Firefox that allow downloading of many (but not all) Internet audio streams.

Yeah I have always "downloaded" a stream whenever I can but not possible this time, so recording it...
What do you mean that a stream is converted to analog (when recording in stereo) by the sound card and then back to digital before Audacity records it?, do all programmes work this way?