Information from the manual:
The Music Machine incoporates two Ferranti devices for digital-to-analogue (DAC) and analogue-tod-digital (A to D) conversion. The part numbers are ZN429E8 and ZN449 respectively. The circuit also include a Motorola [[6850 ACIA chip]] (Asynchronous Communications Interface Adapter) for handling the MIDI channel, two anti-alias filters (one for input and one for output), a discrete microphone amplifier and a headphone amplifier. The clock signal for the ACIA and the ZN449 is provided by a ceramic oscillator.
The incomming signal from the microphone amplifier is sampled to an 8-bit resolution at a rate of 19.444 thoudsand samples per second. This yields an analogue bandwidth of approximately 9.5KHz which is in fact the cutoff frequency of the filters.