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Bit Depth and aac *quicktime aac*
post Jan 26 2013, 17:10
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I have some needledrops, 24/96 *forget the hdtracks now cause i'm learning some new stuff*

andn i use izotope src and mbit to resample and dither to 48/16

i've apparently learned that there is no depth in aac *bit depth*

and i'm curious, is it better to simply just leave all my drops at 24 bits so when encoded for portable use it will be used?

In comparisons i've done when dithered and when just left normal the dithered files *when both are encoded to aac* result in slightly larger file sizes and higher bitrates *of maybe 1,2 o even 3 larger, than when converting from 24 bit sources.

I figured with that being the case it must ignore bit depths and always use 16 bit anyway so I left it at that.

If any experts could provide me insight it would be greatly appreciated as i'd like to know which is better and how much difference it makes *not in terms of listening tests but scienticially*
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post Jan 27 2013, 10:10
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Correction: Dither is not used when resampling. It is used when reducing the bit depth, to prevent the addition of unwanted distortions by the quantization error and add broadband noise instead. This also means that applying dither without doing bit depth reduction is not a good idea.

I haven't used Quicktime encoder for quite some years, but I assume it supports 24bit input. In that case, you only need resampling, and this does not need any dithering. The encoders usually change the bit depth from fixed point to floating point anyway, and as such, it does not matter what it originally is. (Note: this does not mean that it reduces the 24bit to 16bits. both end being represented in 32bit float).

So, which is better? Evidently, given what I've said above, the correct way is with the 24bit file, since the 16bit dithered one has added noise. (Which the encoder might ignore or not, depending on its innerworkings)
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