[SOLVED] Operation with array of bytes

[Fred vS]

Hello everybody.

I have a filled array of bytes and want to do a division for each byte of the array.

This array contains the buffer of a audio-file. (the goal is to change volume before to give the buffer to a other process)

Code: [Select]

var

outbuf : array [0..2047]  of byte  ; 


////// the array is filled with datas...

procedure change_volume_array() ; //// here i want to ajust volume div 2
var x
begin
  x := 0 ;
   while x <  Length(outbuf) )   do begin

outbuf[x]  := round(outbuf[x] * 0.5 );

   inc(x) ;
  end;   
end;


Sadly, i do not have the result i want, i get only strange noise.

Other strange thing, if i do :

Code: [Select]

procedure change_volume_To_0() ; //// here i want to ajust volume to 0
var x
begin
  x := 0 ;
   while x <  Length(outbuf) )   do begin

outbuf[x]  := 0;

   inc(x) ;
  end;   
end;
I attempted to ear nothing but in fact i still ear noise (garbage).

Is it a problem of translation Integer to Bytes ?

If well, what must i do ?

Thanks

[Blaazen]

Your code works well here. Are you sure that input data are correct ?
You can make some output to see what is realy there:

Code: [Select]

var x: Integer;
begin
  while x <  Length(outbuf)    do begin

      writeln(inttostr(outbuf[x]));

      inc(x) ;
    end;       


[Fred vS]

@ Blaazen : Thanks to answer 

Sound library MPG123 gives the procedure stream.volume, so it is very easy to change the volume of  a stream.

But library SndFile does not 

I have googeling to find a soiution how to change the volume in SndFile : NOTHING (even not a tip).

So i was thinking to use the procedure of first topic, but i get only garbaged sound.

Are you sure that input data are correct ?

Yes, because if i do not change the volume, it is perfect (but at volume 1).

[greatUnknown]

Are you sure that the only thing in the buffer is volume data.  It sounds like there is
other information there also, which is getting trashed by the division.
Of course, with no mathematical operations, the sound would play normally.

Also, why would you use round (data * 0.5) when you can use data div 2?

[Fred vS]

Are you sure that the only thing in the buffer is volume data.

Im absolutely not sure. If somebody could give me light about that, i would be very lucky 

Also, why would you use round (data * 0.5) when you can use data div 2?

Coz its easier to change into Trunc inside code 
and coz 0.5 is a example, i use a variable who can be > 1 

[Blaazen]

So what are the data that you send to array? Is it some *.wav file?

[Fred vS]

I have try with some ogg file, but not try yet with common wav.
Gonna try 

[edit] Same garbage with wav files 

[Blaazen]

And the data are still compressed ? If yes, then it makes sense.

[Fred vS]

And the data are still compressed ?

Not understood, i was thinking that wav files where not compressed ?

[Fred vS]

If i add 2 arrays together, like here, no problem, the 2 streams are perfectly mixed ...

Code: [Select]

var

outbuf, outbuf2: array [0..2047]  of byte  ; 


////// the 2 arrays are filled with datas...

procedure mix_array() ; //// here i want to mix 2 arrays
var x
begin
  x := 0 ;
   while x <  Length(outbuf) )   do begin

outbuf[x]  := outbuf[x] + oufbuf2[x] ;

   inc(x) ;
  end;   
end;
But to change volume, it is other story...

[User137]

I think the question is, are you decompressing the audio data after you read it from file? What library/code are you using for OGG?

[Blaazen]

Ah, you edited your post. However, all these files have some header and of course you cannot modify it. Only data can be modified.
For example, here is some minimal description of wav files: http://dracoater.blogspot.cz/2008/11/comparing-2-audio-wav-files.html

[Fred vS]

code are you using for OGG

I use PortAudio, together with SndFile and Mpg123...

Ah, you edited your post. However, all these files have some header and of course you cannot modify it. Only data can be modified.

Do you think that it is not possible to change then the volume or apply some DSP effect ?

[Blaazen]

Yes, it is possible but only on the data. Not to file header.

[Fred vS]

OK, then no solution for now,...