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If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

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If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

Postby Parco » Tue Apr 19, 2011 7:11 am

e.g. Converting from 24bit 96000Hz to 24bit 44100Hz
Then do I still need to dither and noise-shape it anymore?
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Re: If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

Postby Ted Kendall » Tue Apr 19, 2011 8:46 am

Strictly speaking, yes. Any operation on a word generates an output word with more bits, which you then need to reduce to the original length. The brutal way to do this is truncation; the polite way is redithering.
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Re: If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

Postby Parco » Tue Apr 19, 2011 9:57 am

Then do I still need to do the dithering and noise-shaping if the bitsize and sampling rate are both same too, but I've just modified the RMS or peak of the original released songs, e.g. normalized, maximized, compressed, or just boosted the whole volume level?
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Re: If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

Postby James Perrett » Tue Apr 19, 2011 11:27 am

Yes - any operation which can produce a result with a higher word length needs to be dithered before the word length is reduced down again.

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Re: If an audio keep the bitsize same, but resample it from 96khz to 44.1khz

Postby Hugh Robjohns » Tue Apr 19, 2011 11:56 am

To be brutally precise, not every operation results in a longer wordlength, but most do.

However, most operations that do result in longer wordlengths also have an automatic redithering element as an integral part of the process, so it's not something you need to worry about in normal applications.

In your specific case, the sample rate converter that processes your 24 bit, 96kHz file to a 24 bit 44.1kHz file will, end up creating a datastream with much more than a 24 bit wordlength, simply because of the nature of the filtering operation involved.

However, that intermediate long wordlength file only exists inside the SRC process itself, and it is automatically redithered to generate the required 24-bit output.

So technically, yes, dithering is required, but in practice it happens automatically and you don't need to worry about it.

Generally, the only time you need to actively manage the dithering is when deliberately reducing the wordlength yourself -- such as when reducing a 24 bit source to a 16 bit output for a CD or similar.

Pretty much all the other occasions when the wordlength needs to be reduced -- such as when mixing or processing signals in a DAW -- is taken care of automatically by the DAW or plug-in software.

And noise-shaping is a specific type of dithering, it's not a separate process.

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