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Parkin_m

Apr 17 2005, 19:11

Hi, Im new thought i would ask a question on here (not sure if anyone will be able to help)

Im writing a program in c++ that opens modifys and saves a wav file.

i have a function that changes the gain:

CODE

    void processGain(void)
    {
//variables declared
int i;
double gain;
double dB;

cout<<endl;
cout<<"GAIN"<<endl;
cout<<"Enter desired gain: ";
cin>>gain;
//into dB
dB = 20*log10(gain);

cout<<"dB gain of "<<dB<<endl;

for (i=0; i<length; i++)
{
     sample[i]=(sample[i])*gain;
}
    }

the problem with this function is: it changes the gain using a number, then displays the DB change.

i want to be able to be able to have the user enter a dB, then for the program to enter this and reduce/gain by that amount.

johny5

Apr 17 2005, 19:18

If you mean the inverse function, it is:
gain = pow(10,dB/20);

to use pow you should import the math library

Parkin_m

Apr 17 2005, 19:21

do you have MSN? Is there any possiblitly we could have a quick chat on there, or on a chat room?

I would be really grateful!

Parkin_m@hotmail.com

cheers mike

ErikS

Apr 17 2005, 19:22

[redundant post removed]

Parkin_m

Apr 17 2005, 19:24

QUOTE (ErikS @ Apr 17 2005, 12:22 PM)

[redundant post removed]

what does that mean?

Parkin_m

Apr 17 2005, 19:25

If anyone can help, please add me!

HotshotGG

Apr 17 2005, 19:34

Most compilers should come with a standard math library. In order to use the power function you need to make sure you are using standard math library that comes with your compiler. I have one question for you? you speak of adjusting volume if you input a particular set of PCM samples into the program so that it can adjust the gain, but were are your file I/O routines? don't you need to be using something like fstream.h to do binary processing?

I am sure somebody with more programming experience can help you.

Parkin_m

Apr 17 2005, 19:44

QUOTE (HotshotGG @ Apr 17 2005, 12:34 PM)

I am sure somebody with more programming experience can help you.

i only included the part of the program i was having trouble with.
I have a whole class that opens and closes a wav file. this is just a function which edits it. so yes them files are already called from the library.

Otto42

Apr 18 2005, 16:51

QUOTE (Parkin_m @ Apr 17 2005, 12:11 PM)

Hi, Im new thought i would ask a question on here (not sure if anyone will be able to help)

Im writing a program in c++ that opens modifys and saves a wav file.
...
the problem with this function is: it changes the gain using a number, then displays the DB change.

i want to be able to be able to have the user enter a dB, then for the program to enter this and reduce/gain by that amount.

Try something similar to this (this is just psuedocode):

CODE

#include <math.h>

float dbvalue;
cout << "Enter dB adjustment: ";
cin >> dbvalue;

float multiplier = pow(10,dbvalue * 0.05);

for (i=0; i<length; i++)
{
sample[i]=(sample[i])*multiplier;
}

Basically, you take the dB adjustment, and plug it into this equation:
multiplier = 10 ^ (dB / 20);

This turns the dB adjustment into a number which you then want to multiply every sample by. Simple.

Obviously, it's more complex than that. For WAV files, you have an upper and lower end than you have to check for, because you'll be clipping the sound sometimes. So it'll be slightly more complex than the above.

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