Brent Brown wrote:
>
> > I need to know how the sound information is stored in a WAV file and how I
> > can programmatically raise the volume of the sound in a WAV file.
> >
> > Any hint welcome
> >
> > Thank you
> >
> > Duilio Foschi
> >
>
> Not so [OT] because you can do this on a PIC.  Here's some ideas.
>
> Assuming a simple mono 8 bit per sample recording, there is a
> about 20 bytes or so of header information at the start of the file
> and then the audio samples are stored as 8 bit values.  The data is
> "biased" with a 7Fh DC offset so that silence is recorded as 7Fh.
> Kind of like a single rail audio amplifier would be biased at half the
> supply voltage.  For simple play back from a micro with a PWM
> output just send each byte to the PWM register sequentially at the
> original sample rate.  Put an RC filter on the output and
> capacitively couple it to an audio amp.  A little rough by hey - it
> works!  Even play back the header bytes, they go by so fast you
> hardly hear a scratch.
>
> Back to the subject, to digitally amplify a .wav file you would need
> to do something like this for each 8 bit sample:
> - Remove the offset by subtracting 7Fh for data above 7Fh or
> subtracting from 7Fh for data below 7Fh
> - Multiply by your amplification factor
> - Put the offset back in by adding 7Fh or subtracting from 7Fh as
> necessary
> - Store it or play it
>
> You are limited to what you can do in an 8 bit file before clipping.
> Using 16 bit intermediate maths helps by letting you do stuff like
> this: for 10% increase in volume, multiply by 11 then divide by 10.
>
> Brent Brown
> Electronic Design Solutions
> 16 English Street
> Hamilton, New Zealand
> Ph/fax: +64 7 849 0069
> Mobile: 025 334 069
> eMail:  brent.brown@clear.net.nz

tHE LAST CIRCUIT CELLAR HAS INFORMATION ABOUT SOUND REPRODUCED BY PWM...