A question about "rom_fla_rev.spn".

Algorithm development and general DSP issues

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A question about "rom_fla_rev.spn".

Post by lymark » Fri Jan 22, 2021 1:18 am

The following code:
or fladel_138 < 8 ;fladel^ + 138 ;get midpoint address pointer
I think I don't understand what this code does.
'< 'Means to move to the left 8 bits?
Can it be written as `fladel^ + 138`?

Thank you very much who can answer me。 :D

The entire code is as follows:

Code: Select all

;Guitar reverb/flange
;pot0 = reverb mix
;pot1 = flange rate
;pot2 = flange mix
;
mem	fladel	512
;
mem	ap1	150	;reverb allpass at reverb input
mem	ap2	221	;reverb allpass at reverb input
mem	ap3	345	;reverb allpass at reverb input
mem	ap4	431	;reverb allpass at reverb input
mem	rap1	1157	;reverb ring AP
mem	rap1b	2257	;reverb ring AP
mem	rap2	1978	;reverb ring AP
mem	rap2b	1678	;reverb ring AP
mem 	rap3	1850	;reverb ring AP
mem	rap3b	2456	;reverb ring AP
mem	rap4	1234	;reverb ring AP
mem	rap4b	1567	;reverb ring AP
mem	d1	2180	;reverb ring delay
mem	d2	3956	;reverb ring delay
mem	d3	4165	;reverb ring delay
mem	d4	3456	;reverb ring delay
;
equ	fladel_138  fladel+138	;mid pointer to flange delay
equ	fladel_139  fladel+139	;mid pointer to flange delay +1


equ	ramp	reg0	;used to generate ramp waveform	
equ	tri	reg2	;triangle made from ramp
equ	flaout	reg3	;mixed flanger output
equ	fladout	reg4	;flange delay output
equ	mix	reg5	;mix coefficient for flanger
equ	fbk	reg6	;fbk coefficient for feedback around mixed flanger
equ	fract	reg7	;fractional portion of flange read address
equ	k1	reg8	;first coefficient for linear interpolation
equ	k2	reg9	;second coefficient for linear interpolation
equ	temp	reg10	;general temp register
equ	revin	reg11	;input to reverb ring
equ	rfil	reg12	;reverb ring filter register
equ	rt	0.5	;reverb time
;-------------------------------------------------------
;set up lfo for reverb, 0.5Hz, +/-20 samples:
;-------------------------------------------------------
skp	RUN,	LOOP
wlds	0,	12,	160 	;setup LFO0
LOOP:
;-------------------------------------------------------

;--------------------------------------------------------
;prepare mix values from pot2:
;--------------------------------------------------------
rdax	pot2,	1.999	;make pot2 cause mix to be 1:1 at 50% rotation and greater.
wrax	mix,	0	;flange mix is pot2, gain causes saturation limit at approx 1.0, pot2 at midscale
rdax	pot2,	1.0	
mulx	pot2	
wrax	fbk,	0	;feedback is squared pot2, 0 to 1.0	
;--------------------------------------------------------
;write input to flanger:
;--------------------------------------------------------
rdax	fladout,	0.6	;get fraction of flange output	
mulx	fbk		;multiply by feedback function	
rdax	adcl,	0.5	;add inputs * 0.5 each
rdax	adcr,	0.5	
wra	fladel,	0	;write flange delay input, clear acc

;--------------------------------------------------------
; flange rate from pot 1
; as adder value to ramp
; gen, filtered at 0.3Hz:
;--------------------------------------------------------
rdax	pot1,	1.0	;read pot1
mulx	pot1		;square value, range = 0 to 1
sof	0.05,	0.005	;scale to range of 0.005 to 0.55
sof	.001,	0	;scale further to 0.00005 to 0.0055
rdax	ramp,	1.0	;add to ramp value
and	0xbfffff		;allow for rollover (bypasses saturation limiting)
wrax	ramp,	1.0	;write back to ramp register, keep acc
sof	1.0,	-0.25	;subtract 0.25 to center rampwave about 0
maxx	reg0,	0	;get absolute value (make triangle wave from 0 to 0.25)
sof	1.0,	-0.125	;subtract 0.125 to make triangle wave go -0.125 to +0.125
sof	.00015,	0	;scale to filter
rdax 	tri,	0.9999	;filter triangle waveform so that pitch bend does not get too great at high rates
wrax	tri,	0	;write triangle wave to register, clear accumulator

;--------------------------------------------------------
; now formulate delay pointer,
; and pass through to fract calc:
;--------------------------------------------------------
or	fladel_138 < 8		;fladel^ + 138	;get midpoint address pointer
rdax	tri, 0.03125		;add triangle wave modulation, scaled to fit delay range
wrax	addr_ptr,	1.0	;establish address for lower interpolation sample
;--------------------------------------------------------
; address pointer set, now develop fraction of tri:
;-------------------------------------------------------
and	0x0000ff		;mask off integer portion of address, leaving a fractional value in the lowest acc byte
sof 	-2.0,	0	;these operations shift the resulting fractional value to the range 0.0 to 0.999...
sof 	-2.0,	0	;only -2.0 is exact, but it changes sign of shifted value
sof 	-2.0,	0
sof 	-2.0,	0
sof	 -2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	-2.0,	0
sof 	1.9999	,0	;15 shifts, last one is positive, and 1.9999 is nearly 2.0...
wrax	k2,	1.0	;write result as coefficient for second sample read
sof	-1.0,	0.999	;K1 is 1-K2 (or very nearly)
wrax	k1,	0.0	;write result as coefficient for first sample read
;-------------------------------------------------------
;read from first pointer:
;-------------------------------------------------------
rmpa	1.0	;read memory for first sample read
mulx	k1		;multiply by K1	
wrax	temp,	0	;and store in temp, while clearing the acc
;-------------------------------------------------------
;get second pointer:
;-------------------------------------------------------
or	fladel_139 < 8	;fladel^ + 139	;form second pointer
rdax	tri,	0.03125	;add triangle waveform again	
wrax	addr_ptr,	0	;establish address for upper interpolation sample
rmpa	1.0	;read second interpolation sample
mulx	k2		;multiply by K2
rdax	temp,	1.0	;add temp (first value*K1)
wrax	fladout,	1.0	;write the result to the flanger delay output
mulx	mix		;multiply by the mix value
rda	fladel,	1.0	;add the input to the flanger delay
wrax	flaout,	0.0	;write result to flaout and clear acc
;
;-------------------------------------------------------
;do ap smearing to reverb ring allpass filters, modulating them with LFO0, sin, cos, inv sin, inv cos:
;-------------------------------------------------------

cho	RDA,	SIN0,	0x06,	rap1+50	
cho	RDA,	SIN0,	0,	rap1+51		
wra	rap1+100,	0
cho	RDA,	SIN0,	0x07,	rap2+50		
cho	RDA,	SIN0,	1,	rap2+51		
wra	rap2+100,	0
cho 	RDA,	SIN0,	0x0E,	rap3+50		
cho	RDA,	SIN0,	0x08,	rap3+51		
wra	rap3+100,	0
cho 	RDA,	SIN0,	0x0F,	rap4+50		
cho	RDA,	SIN0,	0x09,	rap4+51		
wra	rap4+100,	0
;
;do reverb input allpass filters:
;
rdax	flaout,	0.5	;read value from flanger process
rda	ap1#,	-0.6	;do 4 all pass filters:
wrap	ap1,	0.6	
rda	ap2#,	-0.6
wrap	ap2,	0.6
rda	ap3#,	-0.6	
wrap	ap3,	0.6	
rda	ap4#,	-0.6	
wrap	ap4,	0.6	
wrax	revin,	0.0	;write result to revin, clear acc
;
rda	d4#,	rt	;ring process, read last delay
rda	rap1#,	-0.6	;do 1st ring allpass
wrap	rap1,	0.6	
rda	rap1b#,	-0.7	;do second ring allpass
wrap	rap1b,	0.7	
rdax	revin,	0.5	;read value from input allpass filters.
wra	d1,	0.0	;write the output to the next delay, clear acc
;
rda	d1#,	rt	;do 3 more:	
rda	rap2#,	-0.6	
wrap	rap2,	0.6	
rda	rap2b#,	-0.7	
wrap	rap2b,	0.7	
rdax	revin,	0.5
wra	d2,	0.0	
;
rda	d2#,	rt	
rda	rap3#,	-0.6	
wrap	rap3,	0.6	
rda	rap3b#,	-0.7	
wrap	rap3b,	0.7	
rdax	revin,	0.5
wra	d3,	0.0	
;
rda	d3#,	rt	
rda	rap4#,	-0.6	
wrap	rap4,	0.6	
rda	rap4b#,	-0.7
wrap	rap4b,	0.7	
rdax	revin,	0.5
wra	d4,	0.0	
;
rda	d1+3000,	1.5	;sum weighted taps from the reverb ring delays
rda	d2+1239,	1.2	
rda	d3+2341,	1.05	
rda	d4+302,	0.9	
rdfx	rfil,	0.5
;
mulx	pot0		;multiply reverb output by pot0
mulx	pot0		;do again (as if pot0 was a square function)
rdax	flaout,	0.5	;add flaout
sof	1.999, 	0	;scale gain back up
wrax	dacl,	1.0	;write to right output, save accumulator
sof 	1,	-0.02
wrax	dacr,	0	;write to left output, clear acc

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