Audacity Forum

Hello,

I've downloaded Audacity 2.0.3, running on Windows 7 Pro 64bit.

In *File *Edit *Preferences *Quality I noticed "Sample Rate Conversion" for "Real Time Conversion" was not set to 'best quality - slowest', so I changed it to best quality-slowest, is there any reason the default was not "best quality"?, I presume it's OK to have now set it to "best quality-slowest"?, "Dither" was already set to "None" so I left that...

For "High Quality Conversion" it was already set to "best quality-slowest" so I have left that, however "Dither" was set to "shaped", I think I need to set this to "none" ?, is that correct?

Thanks

PS - I'm wanting the most lossless high quality results as possible...

I'm wanting the most lossless high quality results as possible...

In what kind of show? What is your production and what kind of sound files are you using?

I ask that because if you're trying to edit MP3 files. The highest possible quality is not use Audacity.

Koz

I know MP3 is lossy, I never use MP3 at all...
I use Audacity for "speed" (pitch/tempo) correcting WAV and FLAC files.
Just wanted to make sure those particular settings I asked about are for optimal quality?, and are there any other sneaky settings (like that incorrectly set "dither" setting) I need to change?
Thanks

"Best quality-slowest" and "Dither" set to "shaped" gives the best quality conversion from 32 bit (Audacity's internal format to 16 bit (usually used for export) and for changing the sample rate. This is also the slowest and may be too demanding for real time playback, particularly if you have multiple tracks or a slow computer.

"Medium quality" and "Dither" set to "none" is a lot faster. The "Real time" settings are only used when playing back in Audacity and previewing - they have no effect on processing, mixing or exporting. They are not used if the audio in Audacity is 32 bit (default) and the sample rate of the track matches the Project rate (lower left corner of the main Audacity window).

More information about dither: http://wiki.audacityteam.org/wiki/Dither
More info about the Quality settings: http://manual.audacityteam.org/o/man/qu ... ences.html

Hi,
From what I have always understood "dither" is used when "downsampling"?
When "speed" (pitch/tempo) changing in Audacity I only ever export at the same sample rate as the original files eg. if originally is 16/44.1, I'll export it as 16/44.1, the same goes for a file that is originally 24/48000, once I speed change it I'll export it at 24/48000.
What I noticed was that when "dither" is set to "shaped", if I change the speed of the same original file two different times by the same percentage, and compare the 2 different output files with "EAC Wav Compare", the samples of the 2 different output files will be different to each other, however if I set "dither" to "none", and change the same file 2 different times by the same percentage, the 2 different output files when compared in "EAC Wav Compare" will be identical, I know this is because "dither" is changing the sample rate when set to "shaped", but does this need to be done when my speed changes are being exported at the same sample rate as the orignal file?, does it even matter?, and if so, is the difference between "shaped" and "none" going to be audible? (I ask this as I have dozens of speed changed files made with "dither" set to "none" - using an older version of Audacity).
Thanks

OK...
I just took a 16bit/44.1 file, applied a +2% speed increase, exported it as 16bit/44.1 with dither set to "shaped", I then did the same process with dither set to "none".
I compared the 2 output files and in the silent couple of seconds before and after the music starts in the one with dither set to "shaped" clearly has audible hiss which the one made with dither set to "none" does not....
On quick listen I can't actually hear a difference in the musical content, but yeah the one with dither set to "shaped" definitely has a lot more hiss in the silence before and after the music....
So from what I can tell it sounds better with dither set to "none" ?, but from what I think I understand isn't that the opposite of what you have recommended to me?
Thanks

Shaped dither is recommended when doing the final export of "music". It is not recommended for exporting "silence".
Dither is applied when converting from a high bit depth to a lower bit depth.
Without dither, such a conversion creates harmonic distortion.
With dither, such a conversion adds a little noise.

For "music" there is usually so much more naturally occurring background noise that the dither noise is completely inaudible, but the added harmonic distortion adds an unpleasant and unnatural harshness that is noticeable in very quiet passages.

For synthetic (generated) tones and suchlike, it may be better to use other types of dither (such as "rectangle" which does not add noise during absolute silence) or no dither at all.
The complete solution (avoid harmonic distortion without dither noise) is to keep the audio in 32 bit float format, but then there may be compatibility problems with other applications. 24 bit audio is sometimes used as a compromise solution because harmonic distortion without dither is much less, or noise when using dither is much less.

Attached is a very low level 440Hz sine tone (pure tone) that has been converted from 32 bit float to 16 bit, first with dither and then without dither. It has been greatly amplified to make the difference obvious. And here is the same thing, but at its natural volume. In this sample it begins with a 0 dB (loud) tone so that you can set your playback system to a "normal" level. At a "normal" playback level we are talking about quite subtle differences.

Hello,

Thanks for the samples....

OK I think that's where I am confused. I know dither is supposed to be used when downsampling (going from higher to lower bit depth), but when loading a 16bit file into Audacity (with the float point at 32bit), and I export that original 16bit file as 16bit, is that actually downsampling from 32bit?, or is it working with the file as the original 16bit file?

From what I just worked out, it's actually working with it as a normal 16bit file, not 32bit eg.
I just took a 16bit/44.1 file and saved the first 2 minutes by exporting saved selection with dither "shaped" and another with dither set to "none".
The file with dither "shaped" has different samples to the original file, but the one exported with dither set to "none" has exactly the same samples as the original file (EAC Wav Compare), so it seems dither set to "none" will export the file as it originally was without changing samples....
Maybe that's what you meant when you said "They are not used if the audio in Audacity is 32 bit (default) and the sample rate of the track matches the Project rate (lower left corner of the main Audacity window).", I wasn't sure at first but I think thagt is what you meant there......?

"Resampling" is when you change the "sample rate" (for example, from 48000 to 44100 samples per second).
This is where the "Best quality-slowest" ... setting applies.

"Dither" applies to changing the "sample format" (bit depth) to a lower format - for example from 32 bit to 16 bit.

Audacity always works internally in 32 bit float format.
All processing and mixing occurs in 32 bit float format, including "rendering to a file" (though it is contentious whether Audacity should work in 32 bit float format when rendering 16 bit audio to a 16 bit file).

If you are working purely with 16 bit and are not processing the audio then it is safe to turn dither off because all sample values will be exact 16 bit values and dither is unnecessary. "Cut, Delete, Paste, Copy and Truncate" are simple "editing" commands that do not "process" the sound. Virtually everything else that Audacity does is "processing". "Processing" is anything that requires sample values to be recalculated. Audacity achieves extreme precision when recalculating sample values by working in 32 bit float, but then that leaves the problem that the 32 bit values need to be "rounded" in some way when exporting to 16 bit.

Ah so it does actually work with a file imported as 16bit at 32 bits (I was never sure if that just meant you could import a file of anything up to 32bits, but have it work with the file at it's original bitrate (eg. 16, 24, 32), so it seems then that speed changing 16bit and 24bit files technically does require dither to be set to "shaped", not "none".....
Thanks