Jeff Birt takes a look at digitised speech on the C64 in this first of a series:
Skip to the 20min mark for a bit on Forrest S. Mozer, a physicist who figured out - and patented - ideas for low bitrate speech. Links in the video description, including
Mozer compression (" He first licensed the technology to TeleSensory Systems for use in calculators for the blind and then to National Semiconductor for use in the DigiTalker chip. In 1984, he co-founded Electronic Speech Systems (ESS), and the codec ended up playing speech in Commodore 64 games such as Impossible Mission and Ghostbusters .")
Playback and read in via Datasette, signals will be interpreted as binary value relative to the threshold
Record the stream of ones and zeros
For digital playback, just switch on and off the volume, the SID will produce a short click suitable for low-res, but still understandable audio synthesizes.
(I think, this could even works in BASIC and simple input# for digitizing. It certainly works for live play-through via BASIC.)
You could build a simple phoneme library from this and advance from there.
It’s charming in its simplicity and for utilizing the on/off click artifact of the SID instead of any of the advanced features of the chip. Since any transition from a previous zero state to a non-zero value will produce the click, you can just push the respective bit to the volume register. Nothing is faster than this.
(Since, as mentioned above, it works for live play-through in BASIC, there should be more than enough time left to retrieve audio data from memory and manage phonemes in assembly.)
I recall speech output before the C64. 1979ish on the Apple II - which had a single bit output that used a pure PWM noise algorithm thingy to play back 'samples.
(The original) Castle Wolfenstein was a notable game that used it too.
Memory was key though - those tiny little speech fragments did take up lots of precious RAM!
I think this technique of using the cassette as a simple 1 bit ADC was discovered by a lot of tinkerers including myself circa 1981 and on the Apple II. I remember being a kid and discovering this. Certain sounds like Dizzy Gilespie’s trumpet sounded very good but other things like speech wasn’t so great. Another discovery was that if you placed your finger on the Speaker you could improve the sound quality a great deal. Later I would come to realize that I was effecting a crude low pass filter by using my finger on the speaker cone. It’s intuitive since it tends to muffle the high frequencies when you do that. It was pretty awesome at the time and my father didn’t think it would be possible and yet I was playing digital audio out of the Apple II speaker…
The experiment wasn’t without risk, but I discovered in the Summer of '82 (or maybe '83) that the output transistor for the speaker on my ][+ was strong enough to drive a 12" woofer unassisted. It was quite loud … loud enough to impress me and my friends while we played “Bandits”, and also loud enough to annoy my dad while he tried to watch TV downstairs at the other end of the house!
Nice comparison! I’m reminded of a post made on G+ - here’s the text:
This week, the 6502 and Stephen Hawking’s speech technology.
“At first, the method required a desktop Apple II computer, and later a way was found to bring the computer on-board his wheelchair. “I can communicate better now than before I lost my voice,” Hawking said.”
…
“In 1986, Hawking was given a software package called the “Equalizer,” which had been developed by Walter Woltosz for his mother-in-law. The initial version allowed Hawking to communicate using his thumbs to enter simple commands, selecting words from a database of roughly 3,000 words and phrases, or selecting letters to spell words not contained in the database.”
“The voice synthesis was handled by a Speech Plus CallText 5010 text-to-speech synthesizer built into the back of Hawking’s wheelchair. The voice used by the CallText was based around Klatt’s MITalk, just like DECtalk, but had only a single voice and had been modified and improved by Speech Plus over a 10-year span. A crisp, American-accented voice, it was a clear and well-paced speech pattern that Hawking liked, despite the availability of other voices and synthesis options as time went on.”
For a very little bit more, see the segment just before the 90min mark of this video:
(But watch the whole thing, and you’ll a glimpse of Hawking’s BBC Micro, and as a bonus you will understand the universe.)
Ref:
Stephen Hawking’s voicebox originally a peripheral attached to an Apple II, and finally a Raspberry Pi running an emulation. Professor Stephen Hawking
Ref:
Software was needed for Hawking to select or spell out words and compose sentences.
“However, a computer expert in California, called Walt Woltosz, heard of my plight. He sent me a computer program he had written, called Equalizer. This allowed me to select words from a series of menus on the screen, by pressing a switch in my hand. The program could also be controlled by a switch, operated by head or eye movement. When I have built up what I want to say, I can send it to a speech synthesizer. At first, I just ran the Equalizer program on a desk top computer.”
Ref:
“Equalizer first ran on an Apple II computer linked to a speech synthesiser made by a company called Speech Plus. This system was then adapted by David Mason, the engineer husband of one of Hawking’s nurses, to a portable system that could be mounted on one of the arms of a wheelchair. With this new system, Hawking was able to communicate at a rate of 15 words per minute.”
Ref:
“Back in the 1980s, the now-defunct Digital Equipment Corporation (“DEC”) sold a hardware speech synthesizer based on Dennis Klatt’s research at MIT. These DECTalk boxes were compact and robust, and — despite not having the greatest speech quality — gave valuable speech, telephone and reading accessibility to many people. Stephen Hawking’s distinctive voice is from a pre-DEC version of the MIT hardware.”
