A few questions about BBC Micro sound hardware. Firstly the sound output. Looking at this part of the circuit diagram:
There is 8 KHz marked on the left hand op-amp - am I right in thinking this is a low-pass filter, not band-pass so the lack of low frequencies from the speaker are due to the small size of the speaker and the lack of a baffle for it?
Then, the stage before, we have a virtual earth mixer with one input from the 1Mhz analogue in pin and one from the speech chip but two from the SN76489, one reasonably direct and one via an op-amp circuit:What is the op-amp (part of IC17) with D2 and R2 doing and why are we mixing the output of this into the final sound output as well as the direct output from the SN76489?
B-Em also emulates various other other hardware that produce sound. The Music 5000 is separate in that, when the original hardware is used, it has its own output and would normally be connected to a separate, stereo amplifier. But there is also SID, a DAC connected to the printer port and Paula. Would the real hardware versions of these feed into the mixer above, for example via the 1Mhz bus, and therefore share both the filter and the limited frequency response of the speaker, or do any of them have independent outputs?
Then, the stage before, we have a virtual earth mixer with one input from the 1Mhz analogue in pin and one from the speech chip but two from the SN76489, one reasonably direct and one via an op-amp circuit:
B-Em also emulates various other other hardware that produce sound. The Music 5000 is separate in that, when the original hardware is used, it has its own output and would normally be connected to a separate, stereo amplifier. But there is also SID, a DAC connected to the printer port and Paula. Would the real hardware versions of these feed into the mixer above, for example via the 1Mhz bus, and therefore share both the filter and the limited frequency response of the speaker, or do any of them have independent outputs?
Statistics: Posted by Coeus — Sun Jan 21, 2024 12:56 am