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More than 8 octaves? #23

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fawtytoo opened this issue Nov 16, 2022 · 1 comment
Open

More than 8 octaves? #23

fawtytoo opened this issue Nov 16, 2022 · 1 comment

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@fawtytoo
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fawtytoo commented Nov 16, 2022

OPL is limited to 8 octaves by hardware design. Could this limit be lifted?

@fawtytoo fawtytoo changed the title More than 7 octaves? More than 8 octaves? Nov 16, 2022
@fawtytoo
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fawtytoo commented Mar 28, 2024

I made the common mistake of referring to the frequency blocks as "octaves". However ...

I've been studying this. The limitation is NOT the number of blocks but the range of frequencies within each block. So the range within each block which would need to be doubled for block 7 to reach midi note 127 (currently wraps at note 115). To do that, the f_num would require 11 bits instead of 10. This could be achieved using 2 spare bits available in register B0 (bits 6 & 7). Bit 6 could be the extra required bit for f_num, and bit 7 could be used as a test bit so the "feature" could be turned on/off.

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