Re: [fluid-dev] Purpose of dither?

[Z F]

--- Miguel Lobo <address@hidden> wrote:
> 
> I'm with Mihail on this one: turning off dithering would serve no
> purpose.
> The moment you truncate certain signals without dithering you will be
> introducing high-energy harmonics and nothing you do later will get
> rid of
> them.  Therefore, if you are going to truncate, you *always* want
> dithering.

It does not matter if you add random float to a float and truncate or
trancate and add a random bit, the outcome will be exactly the same
sequence of bits so it does not matter, you can always add dither
later.

Write it out... 

trun(signal + noise) = trun(signal) + noise'

notice that noise' is not the same as noise, but the equality holds
so one can do what can not be done -- remove undesired harmonic
after truncation. (Or more specifically, for every noise you add before
truncation there exists a noise which can be added after truncation,
such that the equality holds. This follows from the properties of the
plus operation.)

Thus, my point --- do it at the last stage, otherwise you will be
dithering the noise too, which I do not think is the goal.

In other words,

SoundEffect(SoundEffect(signal)) + noise

is better than

SoundEffect(SoundEffect(signal+noise)+noise) + noise

See the difference? more noise in the latter case...

ZF



       
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