audio sampling rate question

Ben Bradley wrote:
(someone wrote)

>>>   This doesn't sound right. If you want the best quality possible in
>>>the final 16-bit signal, look into dithering and noise-shaping rather
>>>than doing rounding, and it's best to do all your processing in
>>>floating point (that way you can change the level to any arbitrary
>>>value, rather than only in the 3dB steps that bit shifting gives).
>>>   OTOH, the difference can be subtle, and many people can't tell even
>>>under the best listening conditions.

It isn't hard to do other step sized, but I didn't so far.
Just multiply by some number before shifting.  Even a 32 bit
int should be enough, but definitely 64 bits.

>>I thought about it, but so far I haven't tried.  By finding the
>>peak and appropriate shifting, the quietest parts aren't so far down.

>>It is a recording with a live audience, and the background isn't all
>>that quiet, anyway.  It would be nice, though.  Do others do it?

>    Yes, I'm pretty sure most all audio editing software (everything
> from Audacity to Pro Tools) have been doing it as I described for many
> years now.

This was pretty simple and free.  This is personal, and the
budget is low.

>    It might be easier to write some script file for an audio editing
> program to do what you want. I don't know what programs have what
> features nowadays, but the old Cool Edit 2000 has/had scripting so you
> could do several automated things with audio files.

If I want to add dither can I use an array of some reasonable
length as a periodic data stream?  Generating enough random
numbers for a whole CD might take a while.

-- glen

On Sat, 17 May 2008 22:39:00 -0800, glen herrmannsfeldt
<gah@ugcs.caltech.edu> wrote:

>Ben Bradley wrote:
>(someone wrote)

...

>>>It is a recording with a live audience, and the background isn't all
>>>that quiet, anyway.  It would be nice, though.  Do others do it?
>
>>    Yes, I'm pretty sure most all audio editing software (everything
>> from Audacity to Pro Tools) have been doing it as I described for many
>> years now.
>
>This was pretty simple and free.  This is personal, and the
>budget is low.

   Audacity is free, you might want to play around with it:
http://audacity.sourceforge.net/

>
>>    It might be easier to write some script file for an audio editing
>> program to do what you want. I don't know what programs have what
>> features nowadays, but the old Cool Edit 2000 has/had scripting so you
>> could do several automated things with audio files.
>
>If I want to add dither can I use an array of some reasonable
>length as a periodic data stream?  

   since it's likely "below the threshold of hearing", a second's
worth of random numbers (44,000) ought to do (if it's loud enough to
hear, the ear will be able to hear the repeated nature of the noise),
but a simple what's-it-called, 'congruence' random number generator
can generate adequate numbers with minimal code execution per sample.
If you filter the noise for noise-shaping, the filter code will take
more CPU cycles.

>Generating enough random
>numbers for a whole CD might take a while.
>
>-- glen