Normalizing in Samplers after UV22?

Robert Katz Leave a Comment

From: James Trammell

My comments are:

Bob, I have some instruments I want to sample with my sampler. It has an AES input, so instead of using the cheap A to D on my sampler, I’m using my Apogee AD-1000 with UV22. I have my sampler normalize my samples as I take them. Because I’m normalizing, should I sample with UV22 off and use the AD-1000’s flat dither instead? Or do you think it’s ok to use UV22? I know additional processing of digital data after UV22 encoding is frowned on, but does that include normalizing? If your answer is “don’t use UV22 if you plan to normalize” thats fine with me. I just want to do it right and be mathematically correct. Please keep up the good work informing us all on digital matters.

Dear James:

Hi…. Thanks for your comments.

It’s a good idea to use the superior external A/D. That’s what you’re doing right.

But you suspected correctly. The rest is actually backwards! The last step in the chain of processes should always be the wordlength reduction, along with dither. With a 16-bit sampler you’re damned if you do, damned if you don’t, because you will eventually be using the samples again in your digital mixer and will eventually be adding another stage of veiling dither to it. Instead of normalizing in the sampler, which makes the sound grainy and harsh, and loses depth and stability, you should raise the gain of the source within the A to D converter until the highest peak hits zero. Then dither, then feed the sampler, and don’t change the gain or process again until you have to. If you had a 24-bit sampler, you would not need to dither except at the 24th bit level, which barely changes the sound.

So many of the other manipulations within the samplers (e.g., pitch shifting) also affect the quality of the sound. But if you can’t avoid that, that’s life. Nowadays many plugin samplers use double-precision 48-bit internal calculations and internally dither to 24 bits on their output. This will do the least damage to the sound.

Hope this helps,

Bob

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