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Joined: Nov 2002
Posts: 10
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Joined: Nov 2002
Posts: 10
Hi everyone,

I noticed that when I view waveforms being output from mame, they have a very strong DC positive offset. However, when I play TMS5220 speech from the M1 app (which uses mame code) it has a mean of 0 and therefore has no offset. You can see in this screenshot, Gauntlet is speaking "Traps make walls disappear" with mame on the left, and with m1 on the right. The waveform on the right is much "better".

http://tinyurl.com/pwr2bba

I tried setting all the K parameters to 0 to see the raw excitation filter, and I see this:

http://tinyurl.com/n2zbl38

The voiced frames are completely positive, but the unvoiced frames have a zero mean. You can see, every place in the waveform that goes negative are samples created from the random noise generator (unvoiced frames with a pitch of 0).

I am wondering why is there this offset, and does anyone know of an easy way to get rid of it? I cannot simply subtract the average of samples because the unvoiced ones do not have the offset...

Thanks!

Last edited by patrick 99e99; 02/11/15 03:49 AM.

Patrick J. Collins
Joined: Mar 2006
Posts: 1,047
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Very Senior Member
L
Joined: Mar 2006
Posts: 1,047
This is normal. The voiced frames with k coeffs zeroed SHOULD be always positive with the tms5220.
The chirp rom in the tms5220 is different from the older tms5100 chirp ROM in that it is entirely on one side of the center-line, meaning it has a significant dc offset. The highest bit (d7) of the tms5220 chirp ROM is NEVER set. The tms5100 chirp ROM however does use bit d7 and is more or less balanced around the center-line.

M1 uses older MAME code where it used the tms5100 chirp ROM for everything including tms5220, and this is wrong. (we didn't know any better back then, that was before the tms52xx chips were decapped) If you update M1 to use the chirp ROM from the decap, it will sound the same as MAME does now.

LN


"When life gives you zombies... *CHA-CHIK!* ...you make zombie-ade!"

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