What Dithering to use?

[JumpingJackFlash]

I've got to dither down some of my audio tracks from 24 bit to 16 bit, in order to put them on CD.

One uses real istruments that were recorded, others use synthed and sampled sounds, It's mostly acoustic music of a film-music nature, not all electronic stuff. There is no noise lower than 30hz on any of them (as I remove this with a high-pass filter).

My question is; which dithering algorithm is best?
I'm on a PC, with Logic Audio Platinum 5.5, and Sound Forge 6.0 available.

Logic offers 3 dithers:
POW-r #1 (Dithering)
POW-r #2 (Noise Shaping)
POW-r #3 (Noise Shaping)

And SoundForge offers more dithering options:
Rectangular (1 bit peak-to-peak)
Rectangular (2 bits peak-to-peak)
Triangular (2 bits peak-to-peak)
HighPass Triangular
Gaussian (2 bits RMS-to-RMS)

And noise shaping options:
Off
High-Pass Countour
Equal Loudness Countour

I'm afraid I have no idea what any of this means, and generally very little knowledge of dithering at all.
What dithering would be best for me to use, to make my tracks sound the best of a variety of setups.

Any and all help is appreciated!

[IIRs]

Here's the dither quote I always post, its the best explanation I've yet seen:

Here's a simple thought experiment that explains why dither is necessary and how it works. Lets create a basic A/D converter. We'll make it sensitive to DC and bipolar, so it responds to both positive and negative analogue inputs, and we'll give it a very big LSB threshold of 1 volt to make the numbers easy. We'll construct our ADC so that an analogue source over the range between +.5 volts and 1,5 volts produces an output of 1, and so on. If, without applying any dither, we present a 0.25 volt DC (continuous) signal to the input of the ADC, the output of the ADC will be a string of zeros. In fact any signal between -0.5 and 0.5 volts will result in an ADC output of zero. Any information below the LSB threshold is completely lost.

Remove the 0.25 volt signal and apply dither to the input of the ADC in the form of a completely random signal (i.e.,noise) centred around 0 volts. Its peak amplitude randomly toggles the LSB of the ADC. The output of the ADC will be a stream of very small random values. However the average of all these values will be zero.

Now lets apply our 0.25 volt signal again (with the dither on). The two analogue voltages sum together, the dither and our signal. At each sample point (in time), the 0.25 value of our analogue source is added to the random dither value. The output stream wil again look like a stream of very small random numbers, but guess what? The AVERAGE of all those numbers will now be...you guessed it, 0.25. We have thus retained the information that was previously lost (even though its buried in "noise"). In other words, our resolution has improved. The conversion is still essentially random, but the presence of the 0.25 volt signal biases the randomness. Put another way, the characterization of the system with dither on is transformed from completely deterministic to one of statistical probability. The periodic alternation of the LSB between the states of 0 and 1 results in encoding a source value that is smaller than the LSB. In other words, on the average, the LSB puts out a few more ones than zeros because of our +0.25 volt signal. We say that dither exercises or toggles or modulates the LSB.

With the dither on, we can now change the input signal over a continous range and the average of the ADC will track it perfectly. An input signal of 0.371476 volts will have an average ADC output of (the binary equivalent of) 0.371476. The same will hold true of inputs going over the LSB threshold: an input of 3.22278 will have an average ADC output of 3.22278. So not only has the dither enhanced the resolution of the system to many decimal places, but it has also eliminated "stepping" quantisation effects!

As I understand it, the main differences between flavours of dither lie in the techniques used to make the dither noise itself less audible: Bob Katz recommends auditioning different dithers for each recording to determine which is most suitable!

I haven't gone that far yet, but ever since I read his book I've been meaning compare Tracktion's built-in dither to some of the other ones available..

One thing Bob Katz also says however is "..if the mix isn't good, or the music isn't swinging, then dither probably doesn't matter very much."

I would suggest you either do some scientific listening tests, or just choose one of the noise-shaping options and don't worry about it any further.

[donkey tugger]

Can you tell me which one was used on The Stooges, 'search and destroy'? That's the dither I'm after.

[VitaminD]

Can you tell me which one was used on The Stooges, 'search and destroy'? That's the dither I'm after.

I dont remember that episode..

[chagzuki]

Can you tell me which one was used on The Stooges, 'search and destroy'? That's the dither I'm after.

[IIRs]

Can you tell me which one was used on The Stooges, 'search and destroy'? That's the dither I'm after.

[JumpingJackFlash]

Ok, I know it might be quite technical, but could someone please give me a basic idea of the differences between the various types of dithering available? - And what is Noise Shaping? - Is this always a good thing to enable?

Thanks!

[shamann]

This site might offer some answers:

http://audio.rightmark.org/lukin/dither/dither.htm

[pgarrison]

Hi--

As others have suggested already, the best thing to do (with everything audio related) is use your ears. I'm assuming you're just talking about burning a CD for personal listening. If you are thinking of dithering a CD you want to have duplicated, I would caution against it. Instead, send your tracks to the Mastering engineer is 24-bit format and let him/her do the dithering for you.

[kritikon]

Depends what you're doing. If it's for personal use, if your mixes are fairly dense, I personally see no point whatsoever in dithering. Maybe there are a few delicate petals amongst us who make subtle, sparse extremely dynamic music with long evolving quiet tails in nice quiet sections with nothing but a little carefully recorded reverb - in which case, I'm sure dithering might be useful.

But c'mon...listen in the Music Cafe, and most of the music there has no benefit from dithering - it's either to dense or just too loud and noisy and frenetic - dithering does nothing to loud music.

Has anyone here actually closed their eyes, switched between dither types and heard any difference? Have they even heard a difference between having dither on and off? Because I haven't.

Probably most here are too bashful to admit to not having any idea what dithering does...I know what it does, but buggered if I can hear what it does on my music

If you had professionally produced expensive music that is going to be professionally mastered, then you may as well get those master engineers to dither it for best possible results. But home-produced music, compressed by 5 or more dB then limited to within a rectangle of its life, with layers and layers of synths, pounding drums lots of FX with an RMS that probably rarely goes below 15....you point out to me where dithering is going to make any difference in there.

[dramsenik]

This site might offer some answers:

http://audio.rightmark.org/lukin/dither/dither.htm

I didn't know such a comparison existed on the net.

Thanks for this great link!