Gearslutz.com - View Single Post

dale116dot7 · 18th June 2009

Yes, that is the assumption there. If the AES Blesser paper (the one describing the hardware of an audio processor) describes the EMT250 processor, then the DSP does have the primitives needed to make an oscillator and fiddle with addresses. Something like the M200/PCM70/480L, also the Lexichip1 and 2 requires the host to do it. Since the service manuals for the 480L and LXP15 tell you that the slave Z80 is used to implement the pitch shift and chorus functions, as well as ramped coefficient adjustments, I'll take the manuals at their word.

I've done my LFO's on the host, though I plan on moving that over to the DSP when I get around to it. I did it on the host because it was just faster for me to write it that way. The only problem I have with that approach is that for a single chorus, the update rate is fine, when you have half a dozen of them, I can only update them at about 2kHz or so - and at high chorus rates, you get modulation noise at that frequency. I used the serial host interface, and that is the limiting factor. Had I used the faster parallel host interface and a processor with DMA, I could have easily done the chorus functions on the host, with a 1WC or maybe at most 2WC update of all of the chorus values.

18th June 2009	#112
dale116dot7 Lives for gear Joined: Dec 2003 Location: Calgary, Alberta Posts: 816 Thread Starter	Yes, that is the assumption there. If the AES Blesser paper (the one describing the hardware of an audio processor) describes the EMT250 processor, then the DSP does have the primitives needed to make an oscillator and fiddle with addresses. Something like the M200/PCM70/480L, also the Lexichip1 and 2 requires the host to do it. Since the service manuals for the 480L and LXP15 tell you that the slave Z80 is used to implement the pitch shift and chorus functions, as well as ramped coefficient adjustments, I'll take the manuals at their word. I've done my LFO's on the host, though I plan on moving that over to the DSP when I get around to it. I did it on the host because it was just faster for me to write it that way. The only problem I have with that approach is that for a single chorus, the update rate is fine, when you have half a dozen of them, I can only update them at about 2kHz or so - and at high chorus rates, you get modulation noise at that frequency. I used the serial host interface, and that is the limiting factor. Had I used the faster parallel host interface and a processor with DMA, I could have easily done the chorus functions on the host, with a 1WC or maybe at most 2WC update of all of the chorus values.