Oversampling 8KHz to 44.1KHz

Erik,

> Sorry, thats just plain bad advice.

I'd figured that out already, by reading the other advices :)

> "The day Microsoft makes something that doesn't suck is probably the
> day they start making vacuum cleaners." -- Ernst Jan Plugge

Nice ;-)

Rob Vermeulen wrote:
> Erik,
> 
>>Sorry, thats just plain bad advice.
> 
> I'd figured that out already, by reading the other advices :)

If you're strapped for processing resources, and if you are processing off-line 
data (that is, the sample rate converter is not between an A/D and a D/A - for 
example, you could be streaming A/D to disk), then you might consider converting 
8KHz to 44.0KHz instead of to 44.1K.  This will shift the frequencies down, but 
for the typical 8K-sampled signal (voice), the shift will not likely be noticed. 
  I dunno how it might affect modulated signals (i.e., fax/modems) but even that 
might be able to tolerate the frequency shift.

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
People think it must be fun to be a super genius, but they don't realize
how hard it is to put up with all the idiots in the world - Calvin

On 2004-11-03 14:39:31 +0100, Jim Thomas <jthomas@bittware.com> said:

> ...then you might consider converting 8KHz to 44.0KHz instead of to 
> 44.1K.  This will shift the frequencies down,

Just some nit picking: it will actually *scale* the frequencies. It 
will shift the pitch...
-- 
Stephan M. Bernsee
http://www.dspdimension.com

ggabe wrote:

> There's a 8KHz audio sample rate I want to convert up to 44.1KHz
> sample rate. What's the right approach to keep Mr. Nyquist happy?

No one's mentioned Secret Rabbit Code for sample rate conversion.  I 
haven't tried it, but from the web site it looks like good stuff.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

If the data sample isn't too long, you might try "Perfect Interpolation".

In article <10ohv6pln7psi4a@corp.supernews.com>, Tim Wescott 
<tim@wescottnospamdesign.com> wrote:
>ggabe wrote:
>
>> There's a 8KHz audio sample rate I want to convert up to 44.1KHz
>> sample rate. What's the right approach to keep Mr. Nyquist happy?
>
>No one's mentioned Secret Rabbit Code for sample rate conversion.  I 
>haven't tried it, but from the web site it looks like good stuff.
>

Stephan M. Bernsee wrote:
> On 2004-11-03 14:39:31 +0100, Jim Thomas <jthomas@bittware.com> said:
> 
>> ...then you might consider converting 8KHz to 44.0KHz instead of to 
>> 44.1K.  This will shift the frequencies down,
> 
> 
> Just some nit picking: it will actually *scale* the frequencies. It will 
> shift the pitch...

Yes.  I think the only advantage this offers though is that it requires less 
memory for the the filter coefficients.  Using the standard multirate filtering 
tricks (don't multiply by zero, and don't calculate samples that will be 
discarded), the processing time should be about the same.

These days, reduced memory is not much of an advantage.

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
People think it must be fun to be a super genius, but they don't realize
how hard it is to put up with all the idiots in the world - Calvin

Tim Wescott wrote:
> 
> ggabe wrote:
> 
> > There's a 8KHz audio sample rate I want to convert up to 44.1KHz
> > sample rate. What's the right approach to keep Mr. Nyquist happy?
> 
> No one's mentioned Secret Rabbit Code for sample rate conversion.  I
> haven't tried it, but from the web site it looks like good stuff.

Actually, I pretty sure I mentioned it (see my email address below) 
:-).

Erik
-- 
+-----------------------------------------------------------+
  Erik de Castro Lopo  nospam@mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"Always code as if the person who ends up maintaining your 
code will be a violent psychopath who knows where you live." 
-- Martin Golding