Reverse engineering a Hit Clip (2013)

Re:Reverse engineering a Hit Clip (2013) by tialaramex on Monday September 28, 2020 @08:12AM (#24615739)

After more thought it's unclear to me whether this is actually storing PWM. It can make sense to emit PWM even if what you've actually stored is something quite different, because turning PWM into recognisable sounds with cheap electronics is easy.

The PWM described (~8 MHz of one bit PWM) ought to be capable of far better fidelity than we see in Techmoan's video or the linked audio from the blog post - it's pretty similar to (mono) Super Audio CD for example.

So that's why I end up thinking that the interesting part is probably in the chip you can't easily get at. Like maybe it's MPEG audio layer II with a PWM decoder or something.

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Re:Reverse engineering a Hit Clip (2013) by phire on Monday September 28, 2020 @10:15AM (#24616812)

There is no way it's anything as advanced as MP3.

It's probably a simplistic codec that was originally designed for speech and not music, which would explain the crappy audio.

There are a bunch of specialised microcontrollers designed for toys with like a 4bit CPU, a few GPIOs, 64 bytes of ram and a big massive mask ROM (like a few hundred KB) to hold audio data. They are designed for toys were you press a button and the doll speaks a random catchphrase. One of the common chips in the era was the Winbond "PowerSpeech", which used 4-bit ADPCM at 6khz, 8khz, or 12khz

I think Tiger just took one of these MCUs, picked the biggest mask ROM available and put a single 60 second music clip on it.

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