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Does Dither Really Matter?
Conventional audio wisdom says that dither is required whenever you reduce the bit-depth of an audio file. Typically, when reducing a 24-bit mix to 16 bits for putting onto a CD. Dither is a very low-level noise that's added when reducing bit depth, and by definition it's about 90 dB below the music when reducing to 16 bits. Most people would have a hard time hearing noise that's 60 dB below the music, since the music masks the noise. Yet if you ask a dozen audio recording engineers if dither is necessary when going from 24 to 16 bits, every one of them will say Yes. Even the manual for Sony Sound Forge claims dither is important:
If you want to burn a 24-bit audio file to an audio CD,
dithering will produce a cleaner signal than a simple
Some engineers even argue over which type of dither is best, claiming this algorithm is more airy sounding that that one, and so forth. But just because everyone believes this, does that make it true?
To be clear, using dither is never a bad thing, and it can sometimes help on soft material recorded at very low levels. So I'm not arguing against using dither! But I've never heard dither make any difference when applied to typical pop music recorded at sensible levels. I'm merely pointing out that not using dither is never the reason a newbie's mixes sound bad.
To test this for myself - and for you - I created THIS set of test files (11 MB Zip) containing both truncated and dithered versions of the same sections of my pop tune Lullaby. These are the exact steps I followed:
I started with the Lullaby example from my AES Audio Myths Workshop video on YouTube. I rendered it from SONAR at 24 bits and extracted four short sections. I then alternately dithered and truncated each section down to 16 bits, and renamed the files to hide their identity. So lullaby a/b are the same part of the tune, with one dithered and the other truncated. Same for the file pairs c/d, e/f, and g/h. Your mission is to identify which file in each pair is dithered and which is truncated, and email me your choices (email link is on my home page). The dithering was done in Sound Forge using High-pass Triangular dither with High-pass Contour noise shaping.
Added January 25, 2010: The files linked above and the explanation are new, replacing the original file excerpts that switched randomly between truncated and dithered. Some people fairly criticized that as an invalid test, because you're not able to hear the same music with and without dither. So with the new files this is now a valid test.
Added January 19, 2008: A forum friend and I did some extensive listening tests to compare dither, jitter, and A/D converter quality. My report is HERE in Lynn Fuston's 3dB audio forum.
Ethan Winer has been an audio pro and skeptic for most of his adult life. He now heads up RealTraps, where he designs acoustic treatment products for recording studios and home listening rooms.
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