I found SoX and used it for the frequency conversion w/low pass filtering.

I created a bunch of test ROMs that utilize the original MAME Berzerk samples as well as the various built in voices on the Mac. To create the samples for the Mac voices I used the Speech System Preference panel, selected each voice and ran the script create.sh (in the samples folder of the attached source code), which creates audio files for each word.

I then ran convert.sh, which runs sox to convert the sample to a RAW file using unsigned 8 bit @ 2000 hz using a 1000 hz lowpass filter. It next runs the file thru raw_to_dpc which converts the sample to 4 bit.

Next ran DASM and built a new build of the digital audio test. I renamed the ROM to the current Mac voice.

Finally I went back to the Speech System Preference panel and selected the next voice and started the process anew.

When all the Mac voices were done, I then ran berzerk.sh to convert the Berzerk samples and compiled a new build of the ROM. The difference between berzerk.sh and convert.sh is the first looks for *.WAV sound files to convert, the second looks for *.AIFF sound files.

The parameters I used for for sox are:

sox --norm input -b 8 -u output lowpass 1000 rate 2000

--norm = normalize the audio

input = name of sample to convert

-b 8 = 8 bit data

-u = unsigned data

output = converted sample

lowpass 1000 = applies filter

rate 2000 = resamples to 2000 hz.

I also calculated out the DataFetcher increment based on the 2000 hz. The result of which was (256 * 2000) / (262 * 60) = 33. A value of 33 for the increment means each sample is played back over 7.75 scanlines (256/33).

test roms with Berzerk and Mac voices

VoiceTests.zip

Source

DigitalAudio 2.zip