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Summary Submitted by andym00 on 10 March 2012
A first sample of synthesising 3 voices of pulse wave audio at 15.6Khz, with the screen on even..
Massively reduces the number of interrupts used, so although 15.6Khz is the playback rate it's generating interrupts when the waveforms actually change..
Currently just running 3 voices and bolted onto a NES APU interface to allow it to playback NSFs.. This is totally unrelated to Mr.SIDs NES stuff, although the 2 could potentially work together for doing VRC6/MMC5 tunes..
Space toggles through screen on/off and/or timing bars on the NMI so you can see what's actually going on..
F1 - Toggles between the waveform display and something else..
F3 - Toggles 2Mhz mode on 128s..
As you can see from the CPU loads, it doesn't take a lot of time to synthesise several voices of good audio ;)
There's no fancy CPU loads, just the 4 counters..
NSF - Actual NSF music driver..
APU - Translating NES APU registers to my internal voices, and dynamically balancing the levels..
VOL - Volume table building
SYN - The hard work bit, actually setting some bits and stuff..
The above values are all measured in scanlines, but remember that this is how long it took in the previous 256 sample window, not in the last displayed frame.. So 100% = 256 in this case..
Anyway.. Just a preview of the whole thing..
Long term goal is proper music system to allow adding several extra voices to normal SID compositions without needing masses of CPU to do it, which this achieves nicely..
And seriously, 15.6Khz with the screen on doesn't sound as bad as you might imagine, or take as much time as you think..
Although this uses only 3 voices, the system is good for up to 8, but by then you'll have problems with balancing your dynamic range on each voice if playing out through D418, and this method doesn't work well with the 8Bit voice DAC methods.. Already this is dynamically altering the levels to make the best use of the limited range available, so you do hear some 'pumping' here and there..
Enjoy..
Andym00 |
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