In a dither about dither

[BehindEnemyDeadlines]

Hi! I'm creating and manipulating 24-bit files. When manipulating them my hoste uses floating point temporary files and, when I save the file when I think I'm done, of course it saves to fixed or whatever the appropriate vocabulary is. I'm not intending to mix this stuff down to 16-bit so should I bother dithering and if so, when? Before I save? Trouble is, what if I come back to a file and see that there's more I want to do to it?

[Breeze]

Covers a lot of ground but does eventually compare dithering to truncation with interesting results.

[BehindEnemyDeadlines]

Covers a lot of ground but does eventually compare dithering to truncation with interesting results.

Thanks. I have bookmarked the link but aren't there lively debates raging, or at least haven't there been, about this workshop? I heard that what this guy has to say is fairly controvercial and that lots of people don't buy into it. The confusion and contrary opinions on the subject is partly what's making me unsure how to proceed.

Anyway I read back over my initial post and figured I probably could have written it more clearly.

My understanding of dither is that you shouldn't dither more than once and you should do so after you've done all your destructive processing. I'm creating 24-bit files but I don't intend them to get any smaller than that. I dither before saving because that's when the floating point temporary files get rendered to their fixed format. With a couple of the files I've already saved, I've discovered that I now want to make changes, having already dithered them. What I want to know is, should I re-open them, make the changes I want, thereby introducing more quantization distortion, and then redither or just save not bothering to dither again. Or should I just recreate the projects from scratch?

My other question is how do I avoid this problem in the future? If I save a file thinking I'm done and then want to come back to it to make further changes, what's the least harmful way to do that?

[meloco_go]

There's no reason dither can hurt you.
It may not make a difference, and it would add noise, but with 24-bits you have 144dB of theoretical dynamic range, so why not?
Essentially it makes digital code more robust. Just make sure you set dither at the right bit depth (e.g. don't set dither for 16-bit if you intend to save file at 24-bits).

[IIRs]

You don't really need to bother with dither if you're working with 24 bit audio.

[BehindEnemyDeadlines]

There's no reason dither can hurt you.
It may not make a difference, and it would add noise, but with 24-bits you have 144dB of theoretical dynamic range, so why not?
Essentially it makes digital code more robust. Just make sure you set dither at the right bit depth (e.g. don't set dither for 16-bit if you intend to save file at 24-bits).

Academic question since I would never do that, but what would happen if you did? It wouldn't change the actual bit depth would it. Would it just add noise at -9x DB instead?

[IIRs]

It might just add noise. Or it might also truncate the signal to 16 bit and fill the bottom 8 bits with zeroes.

[shanecgriffo]

i was under the impression that at 24bit no need to dither

[meloco_go]

Academic question since I would never do that, but what would happen if you did? It wouldn't change the actual bit depth would it. Would it just add noise at -9x DB instead?

Yeah, it would add just add more noise. That would also mean that there's no point in saving file at 24-bits.

[IIRs]

i was under the impression that at 24bit no need to dither

Technically you should dither whenever you reduce wordlength, so 32/64 bit down to 24 bit should require 24 bit dither.

But in the real world, 24 bit dither noise is so far below the noise floor of any listening environment, not to mention the amp and speakers and probably also the DAC, that its really not an issue. There are 100000000 better things to worry about!

<edit> make that 010111101011001100000000 better things

[BehindEnemyDeadlines]

i was under the impression that at 24bit no need to dither

Technically you should dither whenever you reduce wordlength, so 32/64 bit down to 24 bit should require 24 bit dither.

But in the real world, 24 bit dither noise is so far below the noise floor of any listening environment, not to mention the amp and speakers and probably also the DAC, that its really not an issue. There are 100000000 better things to worry about!

<edit> make that 010111101011001100000000 better things

So, technically speaking, what should you do if you start and finish at the same word length? Do you dither when done then?

[geroyannis]

So, technically speaking, what should you do if you start and finish at the same word length? Do you dither when done then?

No, there's no need to. You only need to do that just before converting to a lower bit-rate.

[BehindEnemyDeadlines]

So, technically speaking, what should you do if you start and finish at the same word length? Do you dither when done then?

No, there's no need to. You only need to do that just before converting to a lower bit-rate.

But you'll still have introduced quantization distortion by your edits won't you? So what do you do about it? And do you dither when converting from floating point to fixed?

[yairhol]

BehindEnemyDeadlines (long name), you have been answered several times already. You don't dither if you're staying at the same bit rate that your music is in. If you make music at 24 bits, you don't dither to 24 bits. Dithering is only done when moving from a higher to a lower bit rate. That's it.
Have you made any music at 24 bits already? If you did and know what you're doing in regards to recording and mixing, you'd know that there is no audible noise at 24 bits. And if you don't know what you're doing and for some reason you have noise at 24 bits, dithering will not make them dissapear.

[BehindEnemyDeadlines]

BehindEnemyDeadlines (long name), you have been answered several times already. You don't dither if you're staying at the same bit rate that your music is in. If you make music at 24 bits, you don't dither to 24 bits. Dithering is only done when moving from a higher to a lower bit rate. That's it.
Have you made any music at 24 bits already? If you did and know what you're doing in regards to recording and mixing, you'd know that there is no audible noise at 24 bits. And if you don't know what you're doing and for some reason you have noise at 24 bits, dithering will not make them dissapear.

I'm sorry. I probably should have been clearer again. My last question was more academic and motivated by interest than necesity. I just said what do you do if you start and finish at the same word length, which was meant to include hypathetical examples where, for some reason, someone had been forced to start and finish at 16-bit. Is there any way to mitigate noise caused by rounding. Also, I was curious to know what the result in the loss of precision changing from floating point to fixed would be, whether that also introduced noise and what, if anything could or should be done to mitigate it.

I just like to know how these things work even if, in the real world, it doesn't matter because no-one can hear the difference. I'm still curious to know what process or workflow does the least harm or cures the most. Sorry if these questions are agravating.