::
::
:: >
:: > As a value of 200 for BLACKSIZE showed an improvement in resampling, why
:: > does is still got a value as low as 25?
:: >
:: >
:: > Regards,
:: >
:: > --
:: >
:: > Gabriel Bouvigne - France
::
:: Hi Gabriel,
::
:: Increasing BLACKSIZE only improves the sharpness of the lowpass
:: cutoff. For resampling, I dont think we need an extremely sharp
:: cutoff, and maybe a more gradual cutoff even sounds better?
::
:: The problem David discovered (on that mp3.com posting) (aliasing onto
:: lower frequencies) was related to BPC - the number of precomputed
:: convolution functions. LAME was precomputing only 16, but this is now
:: bumped up to 160 in lame 3.87.
::
:: I hope to add something soon which has it precompute the exact amount
:: needed. Does anyone have code which computes the lcd (largest
:: common denominator) of two ints?
::
Frequencies are real numbers, not integral numbers.
And I don't like code like:
if ( Frequency == 44055 || Frequency == 44056 ) Frequency = 2863636/65.L; // NTSC
PCM
if ( Frequency == 31468 || Frequency == 31469 ) Frequency = 2863636/91.L; // NTSC
Hi8 Digital
if ( Frequency == 22254 || Frequency == 22255 ) Frequency = 244800/11.L; // MAC
HQ
if ( Frequency == 11127 || Frequency == 11128 ) Frequency = 122400/11.L; // MAC
LQ
if ( Frequency == 8012 || Frequency == 8013 ) Frequency = 312500/39.L; //
NeXT/Telco
if ( Frequency == 5512 || Frequency == 5513 ) Frequency = 44100/ 8.L; // 1/8
CD
Table index search is done by:
double Factorize ( const long double f1, const long double f2, int* x1, int* x2 )
{
unsigned i;
long ltmp;
long double ftmp;
double minerror = 1.;
double abserror = 1.;
double error;
assert ( f1 > 0. );
assert ( f2 > 0. );
assert ( x1 != NULL );
assert ( x2 != NULL );
for ( i = 1; i <= MAX_TABLES; i++) {
ftmp = f2 * i / f1;
ltmp = (long) ( ftmp + 0.5 );
error = fabs ( ltmp/ftmp - 1.);
if ( error < minerror ) {
*x1 = i;
*x2 = (int)ltmp;
minerror = error * 0.999999999;
abserror = ltmp/ftmp - 1.;
}
}
return abserror;
}
:: I think the number of windows needed
:: is given by: out_samplerate/(lcd(in_samplerate,out_samplerate))
::
:: (44.1khz -> 32khz requires 320 windows, but 48khz->32khz only
:: requires 4!)
::
48 kHz -> 32 kHz requires 2 sets of coefficients. This coefficients are not
the windows. The window function is the same for all sets of coefficients.
You need setup code like:
err = Factorize ( NewFrequency, Frequency, &iNew, &iOld );
if ( err != 0. )
fprintf ( stderr, "(%.6Lf => %.6Lf Hz, Ratio %u:%u, Error %+.3f ppm) ",
Frequency, NewFrequency, iNew, iOld, 1.e6*err );
else
fprintf ( stderr, "(%.6Lf => %.6Lf Hz, Ratio %u:%u) ", Frequency,
NewFrequency, iNew, iOld );
...
for ( i = 0; i < iNew; i++ ) {
k = imuldiv (i, iOld, iNew) - WINDOW_SIZE;
(iNew < iOld ? Calc_Coeffs_Down : Calc_Coeffs_Up) ( Coeff [i], iNew, iOld, i,
k );
}
and transforming code like:
for ( ...; i < ...; i++ ) {
k = imuldiv (i, iOld, iNew) - WINDOW_SIZE;
ScalarWindow ( Dest.fData [i], Coeff [i%iNew], sData + k );
}
--
Mit freundlichen Grüßen
Frank Klemm
eMail | [EMAIL PROTECTED] home: [EMAIL PROTECTED]
phone | +49 (3641) 64-2721 home: +49 (3641) 390545
sMail | R.-Breitscheid-Str. 43, 07747 Jena, Germany
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