Hi all.
I found a bug of MS threshold adjustment, but I don't have a paper
describing the algorithm(*). so I want to someone to check this.
(*) Johnston & Ferreira 1992 ICASSP paper
current LAME calculates mld as
/* setup stereo demasking thresholds */
/* formula reverse enginerred from plot in paper */
for ( sb = 0; sb < SBPSY_s; sb++ ) {
FLOAT8 mld = 1.25*(1-cos(PI*sb/SBPSY_s))-2.5;
gfc->mld_s[sb] = pow(10.0,mld);
}
for ( sb = 0; sb < SBPSY_l; sb++ ) {
FLOAT8 mld = 1.25*(1-cos(PI*sb/SBPSY_l))-2.5;
gfc->mld_l[sb] = pow(10.0,mld);
}
but this is clearly bug, I think. it does not think the sampling frequency.
see the FAAC code, we should bark value of sb, not sb itself.
the code should be like below
/* setup stereo demasking thresholds */
/* formula reverse enginerred from plot in paper */
for ( sb = 0; sb < SBPSY_s; sb++ ) {
FLOAT8 bark = freq2bark(sfreq * scale_band.s[sb] / 576);
FLOAT8 mld = 1.25*(1-cos(PI*Min(bark, 15.5)/15.5))-2.5;
gfc->mld_s[sb] = pow(10.0,mld);
}
for ( sb = 0; sb < SBPSY_l; sb++ ) {
FLOAT8 bark = freq2bark(sfreq * scale_band.l[sb] / 576);
FLOAT8 mld = 1.25*(1-cos(PI*Min(bark, 15.5)/15.5))-2.5;
gfc->mld_l[sb] = pow(10.0,mld);
}
does it fit the paper's algorithm ?
---
Takehiro TOMINAGA // may the source be with you!
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