By Nick

Yes, You Should Dither to 24 Bit

Bit-meterThere’s a lot of noise around whether or not you should dither when bouncing down to 24 bit. But the answer is simple – yes you should.

Without going into the actual mathematics of it (partially because you’ll be hard pressed to find someone who really understands) here’s why.

Word length reduction

When we describe a file as 24 bit or 16 bit, we’re talking about the word length. This literally describes the number of decimal places allowed to mathematically describe an event.

What is common knowledge (in the digital audio community) is that when you reduce the word length i.e. convert 24 bit to 16 bit – you should dither. Why? Because dither helps to better make the transition from a longer word length to a shorter word length. If you don’t dither, your DAW will just indiscriminately chuck out the last 8 bits of data. With it, your DAW will still do that, but a bit more artfully.

Quantization distortion

The reason dither is important is quantization distortion. To put it simply, when chucking out the last 8 bits, your DAW doesn’t know what to do with the last bit – the one that describes the quietest section – and this causes quantization distortion as a result of rounding errors. A gritty, horrible sounding distortion that can affect things much higher up in the dynamic range. It can cause a blurring of the stereo image, phase shifts, lack of detail, lack of warmth – despite occurring at the quietest end of the range, below most people’s hearing, the symptoms are dramatic.

Dither randomises the last bit, creating white noise along the lines of tape hiss. This is far more pleasant to our ears, smooths out the bottom end and prevents all the symptoms listed above.

OK, so you’ve been working in 24 bit all along, and you’re bouncing your mix out at 24 bit to send to a mastering engineer – who will dither when it comes to rendering the 16 bit file – you don’t need to dither right? Wrong.

32 bit float

Probably every DAW at this point works internally at 32 bit float. That means that although your individual track files and project are set to 24 bit, every process that is being undertaken by Cubase/Pro Tools/Logic etc. is happening at 32 bit float. Even a single fader move will mean the DAW is working at 32 bit float.

And that means when you bounce your mix to 24 bit, word length reduction is taking place.

And what do you do when you reduce the word length?

Dither.

It’s important to note however, that this is not the time for your fancy noise shaping dither. That’s definitely down to the mastering engineer. This is just for your garden variety ‘flat’ or triangular dither (commonly described as TPDF).

And word to the wise – your DAW may not automatically dither when you bounce. In order to dither correctly you need to insert a dithering plug-in into the last insert of your master fader (so it’s the last thing to touch your audio).

Hear for yourself

I was recently explaining this to a mixing engineer friend of mine. He was sceptical, having learnt (as most of us did) that dithering to 24 bit was unnecessary, and possibly even harmful. So I suggested a blind test. He sent me the same 24 bit mix – one with a flat dither and one without – labelled A and B.

It didn’t take long to pick out which had been dithered. The dithered mix was more focused, more solid and revealed more detail. He went back and re-bounced all the mixes for the EP for mastering.

Try it for yourself, you might be surprised.

The Art of Making Decisions

I generally prefer to take my time over things. Work on a track, leave it a day, make a few changes, leave it a day, change it again – each time the changes getting diminishingly smaller until I load it up one morning and go “yeah”.

I’m certainly not alone in that approach. But sometimes it’s good to be forced into making decisions quickly, and every now and again a job comes along that reminds me that even when you’ve got the time, sometimes it’s better not to use it.

The Mercedes effect

The biggest job with the shortest deadline I’ve had over the last year was mastering the online content for Mercedes’ flagship ‘Sound With Power’ campaign. Without going into details, I was given a day – maybe two – to master an enormous amount of material. It worked out to about 15 minutes per track.

Granted, the tracks were short, and most of them were very similar to each other, but that’s still an awful lot to get through in a very short time. Certainly no leaving it for a day, coming back to it… Even if I’d had the time, it would have been tortuous to go back and re-do every single track so many times.

So I worked on the first track for an hour or two, decided on a workflow, signal chain and general direction and just ploughed my way through it.

The lesson to learn

The Mercedes campaign wasn’t the first time I’ve had to work like that, nor will it be the last. Anyone who’s ever done any work for film, TV or advertising will know the excruciating deadlines and sky-high expectations commonplace in those industries. But as hard as they are, every time I have a job like that, I find it incredibly informative.

The key is making decisions. Anyone who’s ever mixed anything will know the torture of constantly switching plug-ins and techniques, flip-flopping between often minute variations until you can’t hear straight no more. And then you’re lost.

What jobs like these teach me is the value of making a decision and sticking to it. Treating it like what it is: engineering. Presented with a problem, what’s the solution? What are the best tools to use? And how shall we use them? Great, let’s do that then. Job done.

It’s easy to get caught up in the creative distinctions between different compressor models, different saturation algorithms… With so many digital tools at our disposal, perfection is just an oversampling option away. But the more you play around, the less perspective you have.

Know your tools

The real trick is knowing your tools. Pare down your options. I tend to use only one of two options for everything in my chain. After years of experimentation I’ve narrowed it down to what works best for what job. And when I get it wrong I try the other one. I very rarely have to reach for anything else.

Once you know your tools you can make informed decisions and stick to them. Mix blindness is a far worse enemy than choosing arguably the slightly less appropriate tape saturation.

Our Part in the Mercedes ‘Sound With Power’ Campaign

You might have seen this on TV recently.

It premiered during X Factor on Saturday, in what is probably the biggest ad slot in the UK (other than the final). The sound design was all done by our friends and clients Ithaca Audio, the online mash-up kings. We had nothing to do with the TV ad.

But. There is a strong digital element to this campaign. Users can log on to soundwithpower.mercedes-benz.co.uk and choose between a wide range of sounds and samples to create their own mash-ups similar to the TV ad. The best creation will be shown on telly as part of the follow up campaign.

We’re proud to say that we mastered all the material for the interactive online version.

That’s all we’ll say for now, but there will be a blog post soon with some observations about the lessons that can be learnt from the workflow of this kind of project – lots of material, very short deadlines. Very similar to the experience we had mixing a Spanish language feature film recently.

Until then, enjoy making your mash-ups!