On 7/25/15 10:57 AM, Tom Duffy wrote:
You didn't change the bandwidth.
If the target signal is max 30Hz and you have a 192kHz sampler, you
low pass
at 2x your max frequency (60Hz, but lets say 100Hz for convenience) using
a brick wall digital filter (processed at 192kHz). Then you do a
downsampling
of the signal from 192kHz to 100Hz. Then you end up with lower noise
on the 30Hz signal, but you need to play it back with a 100Hz DAC.
but you can virtually noiselessly upsample it back up to 192 kHz.
just the LPF (done at 192 kHz) is enough to lower the noise on the 30 Hz
bandlimited signal.
and that's not counting noise-shaping.
On 7/25/15 3:25 AM, Peter S wrote:
Okay, a few more thoughts:
On 23/07/2015, robert bristow-johnson<r...@audioimagination.com> wrote:
okay, since there is no processing, just passing the signal from A/D to
D/A converter, there is only one quantization operation, at the A/D.
That's only true *if* it's a non-dithered converter (read: a converter
from the previous century).
if it's "properly
dithered", the error will be well described as "noise" that's white with
DC=0 and AC power decoupled from the input value.
Seems the conceptual misunderstanding here is that dithering does not
mean that the error is "described as noise".
oh dear. that's the whole point of it.
do you understand what the difference between rectangular pdf dither and
triangular pdf dither? what it does to the quantization signal? the
whole purpose is to take whatever nasty non-linearity (which a staircase
function is) and turn it into something that is white (or bandlimited
white), and with it's first two moments decoupled from the value of the
input signal.
Rather, dithering means
that we deliberately *add* noise to the signal (because that has
advantages, see the literature).
<sigh>
--
r b-j r...@audioimagination.com
"Imagination is more important than knowledge."
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