**Type :** Bit-reducer and sample&hold unit

**References :** Posted by tobyear[AT]web[DOT]de

**Notes :**

This is a simple bit and sample rate reduction code, maybe some of you can use it. The parameters are bits (1..32) and rate (0..1, 1 is the original samplerate).

Call the function like this:

y=decimate(x);

A VST plugin implementing this algorithm (with full Delphi source code included) can be downloaded from here:

http://tobybear.phreque.com/decimator.zip

Comments/suggestions/improvements are welcome, send them to: tobybear@web.de

**Code :**

// bits: 1..32

// rate: 0..1 (1 is original samplerate)

********** Pascal source **********

var m:longint;

y,cnt,rate:single;

// call this at least once before calling

// decimate() the first time

procedure setparams(bits:integer;shrate:single);

begin

m:=1 shl (bits-1);

cnt:=1;

rate:=shrate;

end;

function decimate(i:single):single;

begin

cnt:=cnt+rate;

if (cnt>1) then

begin

cnt:=cnt-1;

y:=round(i*m)/m;

end;

result:=y;

end;

********** C source **********

int bits=16;

float rate=0.5;

long int m=1<<(bits-1);

float y=0,cnt=0;

float decimate(float i)

{

cnt+=rate;

if (cnt>=1)

{

cnt-=1;

y=(long int)(i*m)/(float)m;

}

return y;

}

**Comments**

__from__ : kaleja[AT]estarcion[DOT]com

__comment__ : Nothing wrong with that, but you can also do fractional-bit-depth decimations, allowing
smooth degradation from high bit depth to
low and back:
---------------------------------------
// something like this -- this is
// completely off the top of my head
// precalculate the quantization level
float bits; // effective bit depth
float quantum = powf( 2.0f, bits );
// per sample
y = floorf( x * quantum ) / quantum;
---------------------------------------

__from__ : dr[DOT]kef[AT]spray[DOT]se

__comment__ : it looks to me like the c-line
long int m=1<<(bits-1);
doesnt give the correct number of quantisation levels if the number of levels is defined as 2^bits. if bits=2 for instance, the above code line returns a bit pattern of 10 (3) and not 11 (2^2) like one would expect.
please, do correct me if im wrong.
/heatrof

__from__ : resofactor[AT]hotmail[DOT]com

__comment__ : just getting into coding, i've mainly been working with synthedit...but would really like to move on into the bigger arena? any pointers for a DSP newbie-totally not hip on structured programming...yet! :O)

__from__ : gary[at]dmt uk

__comment__ : great algo, works fine.. many thanks

__from__ : catena[AT]neostrada[DOT]pl

__comment__ : Hey, kilelr job on that one you guys!

__from__ : jacalyn[DOT]neely[AT]wybusiness[DOT]org

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