[Asterisk-Dev] zt_tone_def explanation

[el Flynn]

hi there,

in the zaptel.h file, i found the following bit of code:

	Calculate the next 6 factors using the following equations:
	l = <level in dbm>, f1 = <freq1>, f2 = <freq2>
	gain = pow(10.0, (l - 3.14) / 20.0) * 65536.0 / 2.0;

	// Frequency factor 1
	fac_1 = 2.0 * cos(2.0 * M_PI * (f1/8000.0)) * 32768.0;
	// Last previous two samples
	init_v2_1 = sin(-4.0 * M_PI * (f1/8000.0)) * gain;
	init_v3_1 = sin(-2.0 * M_PI * (f1/8000.0)) * gain;

	// Frequency factor 2
	fac_2 = 2.0 * cos(2.0 * M_PI * (f2/8000.0)) * 32768.0;
	// Last previous two samples
	init_v2_2 = sin(-4.0 * M_PI * (f2/8000.0)) * gain;
	init_v3_2 = sin(-2.0 * M_PI * (f2/8000.0)) * gain;

if i'm not mistaken, this has something to do with generating DTMF 
tones. can someone give more insight on what the init_v2_1, init_v3_1, 
init_v2_2, init_v3_2 variables are used for?

and also perhaps what this bit of code does? I think it's used in tonezone.c

thanks a bunch.

Flynn