Recurring artifacts trying to export a sound as 8-bit

Question

I have a number of sound effects from my sound designer, and I'm currently trying to export them as 8-bit WAVs for my game. The advice from Artifacts when exporting sound as 8-bit WAV worked perfectly for the first few, but, for one of them, the "Behemoth walk sound," it's not working.

Fairly bad artifacts appear when I try to do this for the Behemoth walk sound. I've tried deleting all the higher frequencies, but they come back as soon as I hit "save." I've read that applying dither when quantizing helps, but it seemed to have no effect. I've tried these tactics both in Audacity and Audition.

I'm pretty stuck, and this is blocking the next release of the game, so any ideas help.

Here's one of the 16-bit versions of this sound:

https://www.dropbox.com/s/unl926m6alzivcb/Behemoth%20walking%20v2%20volume%20adjusted.aiff?dl=0

And here's a characteristic attempt of turning it into 8-bit: https://www.dropbox.com/s/sb4flrlyl1l8c8a/Behemoth%20walking%20v2%20volume%20adjusted%20audition.wav?dl=0

Answer 1

When you quantize the sound down to 8-bit, there are different algorithms you can use to get there. The simplest-to-implement, naïve algorithm is nearest neighbor. This is basically just rounding the amplitude of the signal at each sample to the closest 8-bit value. Imagine taking a black and white photograph and using a photocopier from 30 years ago: anything brighter than 50% gray comes out white; anything darker comes out black.

The solution is dithering. High-frequency noise is added to the signal so that adjacent sample points are used to help more closely approximate the higher precision amplitude value. Noise shaping helps make added noise less perceptible. Consider that black and white photograph again: a newspaper would print it using a halftone screen, which is a kind of dithering. If you examine it with a magnifying glass, you'll see the pattern of dots, but if you hold it at a reasonable distance, you'll perceive it as a grayscale image, albeit with less detail than the original.

I don't know what free tools might offer dithering, but it's pretty standard with professional grade audio software. I'm pretty sure Izotope RX can do it, and it's a standalone tool.