Need help understanding dithering in Logic

Posted by: DPil

Need help understanding dithering in Logic - 09/22/16 10:49 AM

Hi there,

Okay, the problem is like this: I'm trying to convert a 24 bit 44100hz project into a 16 bit wav file for burning to CD.

When I use Logic's built-in dithering (I believe I used the POWr #3 algorithm) the sound quality of the resulting CD is almost as good as the 24-bit version in Logic. Nothing wrong there.

When I use PSP Xenon's dithering (16 bit, option C) the resulting CD sounds horribly harsh and metallic! Really bad, far worse than you would have got from a 4-track tape recorder in the 1990s!

I must be doing something wrong. This is what I am doing:

1) Place PSP Xenon on the Master channel.
2) Turn on quantize, with bitdepth set to 16, autoblck on, and choose shaping algorithm C.
3) Open the Bounce dialogue in Logic. Choose 16-bit output file (PCM Wav) but select no dithering.

I cannot describe how awful the sound is I'm getting on my CDs! What am I doing wrong?

I always assumed that dithering and bit depth reduction had to be done as a single process. I'm not the greatest mathematician, but I don't see how they could be successfully done separately?

The only factors I think that of might be causing problems are: 1) Logic "normalising" the audio and this interfering somehow or 2) I have Logic's Multimeter plugin on the master channel after Xenon - but surely a spectrum analyser should pass the 32 bit float audio through unaltered?

Please help. I'm running out of blank CDs. Thanks in advance.
Posted by: Adam Taborowski

Re: Need help understanding dithering in Logic - 09/23/16 02:30 PM

Dear DPil,

In my humble opinion - you are doing everything right. There might be some hidden setting in Logic which is the reason of described issue.
And you are right - dithering and bit depth reduction has to be done as a "single process" - to be more precisely - you can not add dither noise after bit reduction - it has to be added before this process.

I recommend trying real-time bouncing in Logic instead offline - or another way if you are using real-time at default. It can be helpful finding the reason of the problem.

You can also try PSP X-Dither (even a demo version) - just to check if the problem occurs only with PSP Xenon.

If you'll have any other questions - please write an email:
adam@pspaudioware.com