[time-nuts] Misuse of word "decimate" (was Re: Short term 10MHz source)

[Hal Murray]

petervince1952 at gmail.com said:
> Could you please clarify then exactly what "decimate" means in this context.

Perhaps an example will help.

Consider an audio input system.  You want 0-20 kHz, so you need 40 k 
samples/second.  You also need a sharp cutoff filter at 20 kHz.

An alternative approach is to sample at 160 k samples/second and implement the 
filter in software.  You still need an external anti-aliasing filter, but this 
one doesn't need to be sharp cutoff - just good enough to eliminate everything 
over 80 kHz.

But now you have 160 k samples/second when you only want 40.  The answer is to 
throw away 3 out of 4 samples.  That's decimation or downsampling.

You can downsample at non-integer rates by interpolating.

You can gain bits/sample with this sort of setup.  I'm not sure how to explain 
it.


-- 
These are my opinions.  I hate spam.