[linux-audio-user] Piano feedback, again bundled

[Anahata]

On Thu, Jan 23, 2003 at 07:27:15AM -0800, R Parker wrote:
 
> I guess the interesting problem is aliasing. Right?
>
Very much so!

If any signal exists at (for example) 30 kHz in the input to a 44 kHz A-D
converter, that appears an audible signal at 14 kHz. An antialiasing
filter has to be flat up to about 20kHz and cut off to a low level by
24kHz, as anything above 24k will alias to below 20k.  That's a very tall
order for a filter.

Assuming a hearing limit of 20kHz again:
At 96kHz sampling rate, the filter has to be flat to 20 kHz and cut off to
a low level by 76kHz.  That's a fairly easy filter to make!

There are some signal processing issues too.  I'm not an expert, but I
believe it's quite difficult to do some types of digital filtering at
frequencies getting close to half the sampling rate. 

-- 
Anahata
anahata at treewind.co.uk       Tel: 01638 720444
http://www.treewind.co.uk    Mob: 07976 263827