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2

Here is an example of what the modern preprocessing Tommy is alluding to actually sounds like: er1.ssd er2.ssd er3.ssd. This is encoded using pcmenc, storing 4-bit volumes for each of the three tone channels in turn, evenly spaced at 35294Hz, so this is 12-bit sampling at 11.7kHz or 4-bit sampling at 35.3kHz depending on how you want to look at it. At an ...


5

Both the DFS and the ADFS did indeed reserve memory for themselves at startup, increasing PAGE; this memory was used to hold the current catalogue and other bookkeeping. For adapting existing tape software two observations are helpful: almost nothing on the BBC was a multiload; and you can turf the [A]DFS out of memory if you don't intend to use it again. ...


6

Here's how the specific routine you posted works. It appears to be using the "4-bit linear" method mentioned on this page. The resulting samples are not truly linear, but it's easy to understand and implement, and good enough for game SFX or speech. We'll analyse this in bottom-up order, starting with the last routine, which simply takes a ...


5

The BBC Micro uses an SN76489, which provides three tone channels each with sixteen volume levels. For speech playback the standard approach is to set the channels in use to a very high frequency and then modulate the volume. For each channel the volumes are a logarithmic scale, where each step is approximately 10^-0.1 as loud as the previous, i.e. around 79%...


13

No, it can not be used to sample audio. As the link you provided says, in 12-bit mode it takes 10 milliseconds to convert a sample, and even in 8-bit mode it takes 4 milliseconds. That results into maximum sampling rate of 250 Hz, which is useless for sampling audio. The low sampling rate indicates the analog input is meant for slowly changing signals, like ...


15

The so-called "1MHz bus" is not actually a separate bus. It is just the set of devices which were too slow to run at the full 2MHz in the original BBC Micro, and which therefore incur a clock-stretched cycle when accessed. These include most of the SHEILA ($FExx) devices, except for the Econet, floppy, Tube, VIDPROC, and memory mapping registers. ...


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