Audacity Forum

If the Audacity Quality Preferences are set to 32-bit float, you will have a 32-bit float track after import.

If you want to import as 16-bit you have to change to 16-bit in Quality Preferences.

This isn't recommended for most purposes because processing edits including Amplify will add dither when the data that has been processed in 32-bit float is returned to the track as 16-bit. Of course you can turn dither off, but then you will get quantisation errors which may sound worse than the dither.

If you process in 32-bit float you will only have the downsampling to 16-bit on export to deal with.

Only your ears can tell you what sounds right.



Gale

Gale Andrews wrote:If the Audacity Quality Preferences are set to 32-bit float, you will have a 32-bit float track after import.

If you want to import as 16-bit you have to change to 16-bit in Quality Preferences.

This isn't recommended for most purposes because processing edits including Amplify will add dither when the data that has been processed in 32-bit float is returned to the track as 16-bit. Of course you can turn dither off, but then you will get quantisation errors which may sound worse than the dither.

If you process in 32-bit float you will only have the downsampling to 16-bit on export to deal with.

Only your ears can tell you what sounds right.


Gale

I think I understand now. I only have three questions left now:

1) If I set default to 32, import a 16 bit track, do some simple editing (like cut+paste), and export at 16 bit without dither, would I end up the same track I imported (sound/quality)?

2) Scenario 1: import as 32 bit, do some complex editing (like amplify), then export as 16 bit without dither. Scenario 2: import as 16 bit, do complex editing with dither, export as 16 bit without dither. What is the difference between the two?

3) Can I use dither while editing, but not when exporting? Is there a way to do that?

KlarkKentThe3rd wrote:1) If I set default to 32, import a 16 bit track, do some simple editing (like cut+paste), and export at 16 bit without dither, would I end up the same track I imported (sound/quality)?

Yes.

KlarkKentThe3rd wrote:2) Scenario 1: import as 32 bit, do some complex editing (like amplify), then export as 16 bit without dither. Scenario 2: import as 16 bit, do complex editing with dither, export as 16 bit without dither. What is the difference between the two?

The critical factor here is that the audio data is being "processed" - that is, the individual samples have their values changed.
Scenario 1: This is not ideal because there will be some "distortion" ("quantize" errors / "rounding errors") when converting from 32 bit float to 16 bit.
Scenario 2: If you apply more than one process, this is not ideal because dither will be applied on each process, which is more dither than necessary, thus more "dither noise" than there needs to be.

Ideally, for applying one or more "processes" to a 16 bit source file, the file should be imported as 32 bit float, processed as required, then exported with dither enabled. Processing 32 bit float data does not apply dither (it is not required) and dither is only applied once (on export when the 32 bit data is converted to 16 bit. This is the default behaviour in Audacity.

KlarkKentThe3rd wrote:3) Can I use dither while editing, but not when exporting? Is there a way to do that?

Currently the only place to enable or disable dither is in the Preference settings.
As nearly all jobs involve some form of processing (whether it be amplifying, fading in or out, equalizing, noise removal, or any sort of Effect) it is generally advised to use the default settings of 32 bit quality settings and dither enabled in the High Quality Conversion settings.

The one exception to this is the case of applying only simple cut/copy/paste type edits (that do not change sample values). In this case the results will be marginally better by switching dither off (but this benefit is small and only likely to be noticeable in periods of absolute silence with the playback volume turned up loud.)

So, to preserve the original sound, if I want to, for example, reduce bass in a 16 bit track... I should import it as 32 bit, do the edit, and export without dither?

I wouldn't say that.
When you Import the file and do nothing, with the actual sample values, then dithering is not necessary.
On the other Hand, any effect that you apply in 32 bit mode will produce sample values in that range to form smooth curves.
As soon as you reconvert to 16 bit, the curvature gets steppy.
This produces Aliasing, i.e. some frequencies are fold back into lower ranges. Dithering tries to even out the odd fractions between values to still provide a smooth curve (measured over time).
The Goal is to apply this dithering only once - it is the last step of the mastering process just before delivering the end product.
There are specialised Plug-Ins out there which provide full control for high Quality dithering.
Internal dithering is of course always turned off.
It's sometimes rather an academic question, which algorithm is the best. Only your ear can decide.
Don't fall into the trap to chase for annoying dithering noises. It drives you mad and makes you paranoic.
A lot of those Plug-Ins have "zoom" functions for the preview in order to make the -70 dB noise audible.
Even if you have found the right shape and frequency Profile in this manner, it want help you. The human Hearing System does not work that way.
Frequency sensivity and the perception of noise that is offending or pleasing depends on the Overall loudness. That's why all those perception curves and loudness meters are essentially good for nothing. Only a Little part of the loudness spectrum will be covered.
Psychoaccoustics introduces every few year a new Parameter to describe the perception of Sound and noise (sharpness, roughness etc.).
Dithering will in any case Sound better than aliased frequencies.

KlarkKentThe3rd wrote:So, to preserve the original sound, if I want to, for example, reduce bass in a 16 bit track... I should import it as 32 bit, do the edit, and export without dither?

To summarise Robert's reply and reiterate my previous reply: Reducing the bass requires "filtering" which is a "process" (it changes the sample values), so it is best to work in 32 bit with dither enabled (which is the Audacity default).

Personally I wish that Audacity would do the "right thing" automatically and so save users from this confusion and simply provides an option in the Export dialogue to provide dither choices on Export.

steve wrote:I wish that Audacity would do the "right thing" automatically and so save users from this confusion and simply provides an option in the Export dialogue to provide dither choices on Export.

You mean, a checkbox that when enabled, over-rides the High-Quality dither Preference being "on"?


Gale

Gale Andrews wrote:You mean, a checkbox that when enabled, over-rides the High-Quality dither Preference being "on"?

No, I mean (as discussed on -devel) that processed audio is always returned to tracks in 32 bit float format (so as to avoid needless and possibly damaging format conversions), and that dither options are provided in the Export Dialogue rather than in Preferences (as they then only apply to export). There would then be no need to confuse users with different track formats - audio track data would always be in its original imported format unless processed. If processed it would always be in 32 bit float format (as processing is always 32 bit float).

The (actual) sample format should also be checked by the export code so that dither is not needlessly applied to data when the format is not being converted to a "lower" format.

Does the Setting of the sample Format make any sense after all?
Since Audacity works exclusively in 32 bit mode, the re-converting in each step (to 16 bit for example) is nothing but destructive.
How about a warning box that informs the user that a conversion to 32 bit float is necessary to apply the current effect.
Maybe with a few Options such as:
- re-convert to <original sample Format> after processing
- Convert to 32 bit permanently (recommended).
and two control Buttons for
x dithering on Export
x Show this warning in case of internal conversion.

How about the Project, are the 16 bit tracks saved as such in the Project itself and thus the aliasing or unnecessary dithering is "mixed down" forever?

Robert J. H. wrote:Since Audacity works exclusively in 32 bit mode, the re-converting in each step (to 16 bit for example) is nothing but destructive.

Exactly my point.

Robert J. H. wrote:How about a warning box that informs the user that a conversion to 32 bit float is necessary to apply the current effect.

"Warnings" are useful when they enable people to avoid dangers (Warning: Mind your head. Warning: slippery road ahead. Warning: Vehicle reversing.)
There is no real point in warning someone of something that is inevitable and unavoidable (Warning: making an omelet will cause eggs to be broken).