Re: [stella] Berzerk Voice

[Mike Mika <mikem@xxxxxxxxxxxxxxxxxx>]

Sorry I'm so late to this, guys!

Eckhard answered it for me, pretty much. I do vary how often it updates the 
voice in some cases.

"Intruder Alert! Intruder Alert!" I stored the one half of the phrase, and 
played it back every 4 scan lines like Eckhard's demo, twice.
"Chicken Fight Like A Robot" I sampled this at a bit less than 4000hz, and 
update about every 4.5 lines (I believe)
"Humanoid must not escape" Same thing here, in an effort to make the 
samples fit, I downsampled below 4000hz until it could be stored in a bank 
+ code, then adjusted the playback rate.

I also had another phrase in there, but it had to be so downsampled it was 
too unrecognizable.
The key is splitting the sample into 4bit, so you can save space. Also, the 
roboticized voices were already downsampled for the arcade game pretty 
well, and I found the word fragments from Berzerk on some random site when 
I did a Google search for "Berzerk .WAV". I used some tools I had from GBC 
sample building to downsample, and then wrote a quick (Redundant to 
Eckhard's tool!) 4bit converter- In this case, it does exactly what 
Eckhard's does, so use his- I wasted some time before realizing Eckhard 
already did the work!

As for the code, there is not much else you need to do other than what 
Eckhard outlined in his SAY.A65 code. That's the way we did it on GBC, as 
well, but on an interrupt during Hblank (GBC) so as to keep graphics on 
screen, etc.

You can get some pretty surprising results, actually. Drum beats, voice, 
etc, can sound pretty good. I found that the quality can be sustained, but 
you sacrifice space.

Again, study Eckhard's demo. It was the catalyst to the whole idea of 
adding voice to Berzerk.

Best,
Mike

At 03:59 PM 8/15/02 +0200, you wrote:
> > Unfortunately, very little in the way of details there. I want sample
> rates,
> > bit depths, etc, darnit! :)  Any chance of getting the author to post here
> > explaining how he did it?
>
> Since Mike said he was inspired by the sampled voice demo that I posted
> to the Stella list in early 1997, I guess it's OK, if try to answer this
> question. ;-)
>
> It's 4 bit at about 4000 Hz. Basically you set the audio control register
> to constantly outputing a high signal, and then quickly change the 4 bit
> volume register. In this example the volume gets changed every 4 scanlines,
> which results in a sample frequency of about 4000 Hz. For the robotized
> voices in Berzerk this seems to work quite well. Since changing the sound
> data so often doesn't leave you too much processing time to generate the
> game display, Mike blanks out the screen while he plays the sampled voices.
>
> Where Mike got the samples from I don't know. But I suppose he just
> downsampled the audio files for the MAME Berzerk emulation or something.
>
> > I'd really like to know what this would sound like, or if it's already
> been
> > done. The hardest part of testing this technique would be generating the
> > data. Parsing a WAV is easy, but determing the average frequency of each
> > chunk would require a Fourier transform or similarly hairy algorithm.
>
> That's an interesting idea, but at 60 changes per second, I fear it
> would sound more like the "talking" of the guy in Little Computer people
> than any recognizable words.
>
>
> Ciao, Eckhard Stolberg
>
>
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