Mastering to MP3 - PSP Xenon - Fraunhofer Codec Toolbox

[Gone To Lunch]

I am in 24-bit DP 9.52 and exploring mastering down to mp3, using a PSP Xenon mastering limiter and a Fraunhofer Codec Toolbox. My question is about dithering to 16-bit pre- and post-fader.


In his review of the Fraunhofer Codec Toolbox plug-in, Sam Inglis, SOS Jan ’14, it says :

“…you place Codec Toolbox in the last insert on your master bus…”

And in the Codec manual it says, section 6.1.4 :

“The encoders in the plug-in will accept an input signal with greater than 16-bit precision, but in such cases the signal will be dithered and truncated to 16-bits prior to the encoding process. The plug-in will not introduce dither at the 16-bit level if the input to the plug-in has been already dithered and truncated to 16-bits”


In his ‘Digital Performer Tips & Techniques - All in a Dither’, SOS Feb ’15, Robin Bigwood says :

“Simply put, the DP master fader is the ideal place to instantiate your preferred bit–reduction and dither processor, because it’s conceptually at the end of the mixing signal chain. However, some care is required to do things right, because it’s all too easy to immediately increase the digital resolution again and undo the plug–in’s good work.

It’s worth looking at this in some more detail, but first I’m just going to give you the two–part solution. First, put your bit–reduction and dither plug–in in a lower slot than any others, so it’s the last plug–in in the signal chain. Then, either keep your master fader exactly on a 0dB ‘unity gain’ position or, if it’s at any other position, or you’ve got it automated for a fade–out, make sure that the insert slot occupied by your mastering plug–in is in a post–fader position. How do you do this? Take a close look at your master fader’s (or indeed any channel’s) plug–in slots. Just to the bottom left of them is a tiny, inconspicuous grey ‘notch’. Hover your mouse pointer over it and the pointer turns into a hand — the notch is draggable! Drag it up to just above the last empty plug–in slot and it should change into a blue divider line. Then drag and drop your mastering plug–in into that empty slot, so that it’s now beneath the blue line. That’s all there is to it.

Now for the explanation, if you’re game. DP carries out all mixing tasks with 32–bit floating–point resolution, regardless of whether your actual audio files are 16– or 24–bit, and even for something as apparently simple as a level cut or boost dialled in with a channel fader. Meanwhile, by default, all DP’s plug–in slots lie in a pre–fader position, which is to say that audio flows into the mixer channel, first through the plug–ins, then through the fader, and on to the output.

Back in our mastering scenario, the dither plug–in is carrying out some really clever maths, effectively distilling (or ‘quantising’) the signal chain down to 16–bit, which is what we need for a CD master. If we place another plug–in in a lower slot fail! Its processing will have caused the digital signal to revert to 32–bit format. Similarly, if the master fader is set to somewhere other than at the 0dB position, and therefore applying some level cut or boost it’s more 32–bit processing and another fail! What we need to do is put the fader before the plug–in, so that the plug–in really is the last thing in the signal chain — and that’s what dragging the plug–in slot divider is for. Plug–ins above the divider are pre–fader, while plug–ins below it are post–fader. So by placing the mastering plug–in post–fader, we make it absolutely the last thing in the signal chain.”

So my question are:

Presumably I should insert my PSP xenon post main fader, followed by the Fraunhofer Codec ?

But if I do, will this cause the signal to revert to 32-bit ?

Would this cause an avoidable un-necessary dithering process ?

[FMiguelez]

I don't know the specifics of that particular plugin, but you might want to do some research about dithering for .mp3....

My understanding is that neither .mp3 nor AAC need any dithering, since they use a totally different process.
Also, you wouldn't reduce the bit depth to 16 bits, but let it do the conversion to lossy formats from 32bFP or 24 bit fixed

Look for relevant posts by Nika Aldrich and Paul Frindle over at Hydrogen Audio or Gearslutz.

If your limiter/dither plugin is anything like Waves' Lx series, then you simply put it at the end of your chain in the master (mix) bus, and set the quantization setting to 16 bits, and then you turn on dither and possibly the noise shaping parameter.
That will take DP's 32-bit floating point signal and quantize it to whatever settings you dialed.

Also, if you want to do your own tests, which I recommend, you can get this free plugin to see for yourself how many bits are being used at any point in your signal chain. It's a little gem, and it's free. I use it all the time for my own tests.

https://www.stillwellaudio.com/plugins/bitter/

[FMiguelez]

Another thing you could do, if all you want is to obtain a good .mp3, is to master your music normally at 24/48 KHz, or even 32bFP/48 KHz (the latter one obviously without dither), and then you take that master and import it into iTunes and do the conversion to mp3 or AAC right there.

You could even print your final master at 32bFP/48 KHz in real time in DP. Then, presumably, iTunes would convert to mp3 from the highest and purest possible source, but all this might be just academic and theoretical, since NOBODY would be able to hear the dither noise from those anyway (unless you play the music at instant-hearing-damage listening levels).

If in doubt, do some ABX tests for yourself comparing different mastering methods and marvel about how you won't succeed. You won't be able to tell which has dither or which hasn't.

[mikehalloran]

Thanks, FM. Much better than anything I was planning to write.

I will never (again) convert to mp3 inside DP. It takes forever and life is just too short. QuickTime and iTunes can do the conversion to mp3 as mentioned but they can convert one file at a time only.

There are a number of apps that can do batch conversion. I use and recommend TwistedWave (5 minutes to convert 2.5 hours of stereo) but it may be pricy for some. DSP-Q 4.4 does this (not yet for 5) and there are others. The so-called “free” converters generally ask you to pony up for “premium” features such as batch conversion.

Likewise, I would avoid “one-trick pony” conversion apps. There are plenty of instances where you want or need to convert audio form one file type to another or strip and rewrite corrupt headers leaving the raw audio intact. I receive audio from outside studios on a regular basis and have no control over the garbage I often receive. DP is often sensitive to the quality of the audio it will process—a good conversion utility saves hours of time.

[bayswater]

QuickTime and iTunes can do the conversion to mp3 as mentioned but they can convert one file at a time only.

Maybe not batch conversion in the strictest sense, but if you select multiple songs in iTunes and select "XXX version" in the File>Create menu, it converts them all, PDQ. "XXX" will be whatever you select as the format for ripping CDs in preferences, which presents a lot of encoding options.

[MIDI Life Crisis]

I've been doing my MP3 conversions from this of late:

https://videoconverter.iskysoft.com

Also great for any kind of media conversion. Don't let the "video" in the name fool you. Many great output options. Well worth every penny!

[mikehalloran]

I've been doing my MP3 conversions from this of late:

https://videoconverter.iskysoft.com

Also great for any kind of media conversion. Don't let the "video" in the name fool you. Many great output options. Well worth every penny!

That does look good and $59 is not bad for a lifetime license.

[Gone To Lunch]

So am I right in thinking I do not need to dither at all, because when I select .wav or .mp3 or whatever, the software doing the converting does not actually require it ?

[MIDI Life Crisis]

I've been doing my MP3 conversions from this of late:

https://videoconverter.iskysoft.com

Also great for any kind of media conversion. Don't let the "video" in the name fool you. Many great output options. Well worth every penny!

That does look good and $59 is not bad for a lifetime license.

It really makes delivery of final video and music mixed a breeze. I do a lot of that for the NFPF and have never had a single issue. BTW, I use PSP Xenon to get the levels right, especially for web releases.