E-Guitar synthesizer in 50 lines of Spin 2

Wuerfel_21

CON
SAMPLE_RATE = 44_100
_CLKFREQ = SAMPLE_RATE * 256 * 24
AUDIO_LEFT = 24+6 ' this pin and the next one will have audio
MAX_PERIOD = 16_000
VAR
long string_length
long buffer_ptr
long exciter_on
long retrigger_ctr
long note_cnt
word string_buffer[MAX_PERIOD]
PUB main() | sample, filter,seed, lpf, hpf
pinstart(AUDIO_LEFT addpins 1,P_DAC_124R_3V|P_DAC_DITHER_PWM|P_OE,CLKFREQ/SAMPLE_RATE,$7F80)
repeat
    repeat until pinr(AUDIO_LEFT) ' wait for DAC ready
    wypin(AUDIO_LEFT addpins 1,(sample sar 4)+$7F80) ' set sample
    if --retrigger_ctr < 0 ' trigger new notes
        retrigger_ctr := SAMPLE_RATE /4 ' time to next note
        string_length := (SAMPLE_RATE / getnote()) <# MAX_PERIOD ' tune string
        buffer_ptr := 0
        exciter_on := 1
    if exciter_on
        sample := getrnd() signx 15 ' during first period, generate noise
    else
        sample := (string_buffer[buffer_ptr] signx 15) ' afterwards, read from buffer
    sample := (sample + filter) sar 1 ' incrementally filter sample
    filter := sample
    sample := clamp(sample)
    string_buffer[buffer_ptr] := sample
    if ++buffer_ptr > string_length ' wrap buffer around
        exciter_on := buffer_ptr := 0 ' also turn exciter off
    if 1 ' E-Guitar amplifier simulation - disable for very dry sound
        sample *= 3 ' gain knob
        hpf += (sample-=hpf) sar 3 ' pre-amp AC coupling
        sample := waveshape(sample)
        lpf += (sample-lpf) sar 2 ' just an LPF to make it less harsh
        sample := lpf
PRI getnote() : r
    case (note_cnt+/12)+//3 ' simple arpeggio
        0: r := lookupz(note_cnt+//3 : 262, 311, 392) ' C4 - Eb4 - G4
        1: r := lookupz(note_cnt+//3 : 207, 262, 311) ' A3 - C4 - Eb4
        2: r := lookupz(note_cnt+//3 : 233, 294, 349) ' Bb3 - D4 - F4
    r >>= 1 ' transpose one octave down
    note_cnt++
PRI waveshape(x) : r ' wave shaping using arctan transfer function
    _,r := xypol($2000,x) 
    return clamp(r sar 15)
PRI clamp(x) : r ' clamp to valid 16 bit range
    return x <# $7FFF #> -$7FFF

Something I wrote to pass an hour or so. It's a basic Karplus-Strong synth with a rudimentary tube amp simulation. It'd probably sound better if there were multiple channels and the decay of the previous note was allowed to continue. Or to play chords, of course.

Rayman

This looks interesting. Is that complete? Looks like it needs some note data somewhere to play something?

Seems could be warped into MIDI player...

Wuerfel_21

@Rayman said:
This looks interesting. Is that complete? Looks like it needs some note data somewhere to play something?

Seems could be warped into MIDI player...

Yea, it just plays a little sequence of notes

Christof Eb.

@Wuerfel_21 said:

CON
SAMPLE_RATE = 44_100
_CLKFREQ = SAMPLE_RATE * 256 * 24
AUDIO_LEFT = 24+6 ' this pin and the next one will have audio
MAX_PERIOD = 16_000
VAR
long string_length
long buffer_ptr
long exciter_on
long retrigger_ctr
long note_cnt
word string_buffer[MAX_PERIOD]
PUB main() | sample, filter,seed, lpf, hpf
pinstart(AUDIO_LEFT addpins 1,P_DAC_124R_3V|P_DAC_DITHER_PWM|P_OE,CLKFREQ/SAMPLE_RATE,$7F80)
repeat
    repeat until pinr(AUDIO_LEFT) ' wait for DAC ready
    wypin(AUDIO_LEFT addpins 1,(sample sar 4)+$7F80) ' set sample
    if --retrigger_ctr < 0 ' trigger new notes
        retrigger_ctr := SAMPLE_RATE /4 ' time to next note
        string_length := (SAMPLE_RATE / getnote()) <# MAX_PERIOD ' tune string
        buffer_ptr := 0
        exciter_on := 1
    if exciter_on
        sample := getrnd() signx 15 ' during first period, generate noise
    else
        sample := (string_buffer[buffer_ptr] signx 15) ' afterwards, read from buffer
    sample := (sample + filter) sar 1 ' incrementally filter sample
    filter := sample
    sample := clamp(sample)
    string_buffer[buffer_ptr] := sample
    if ++buffer_ptr > string_length ' wrap buffer around
        exciter_on := buffer_ptr := 0 ' also turn exciter off
    if 1 ' E-Guitar amplifier simulation - disable for very dry sound
        sample *= 3 ' gain knob
        hpf += (sample-=hpf) sar 3 ' pre-amp AC coupling
        sample := waveshape(sample)
        lpf += (sample-lpf) sar 2 ' just an LPF to make it less harsh
        sample := lpf
PRI getnote() : r
    case (note_cnt+/12)+//3 ' simple arpeggio
        0: r := lookupz(note_cnt+//3 : 262, 311, 392) ' C4 - Eb4 - G4
        1: r := lookupz(note_cnt+//3 : 207, 262, 311) ' A3 - C4 - Eb4
        2: r := lookupz(note_cnt+//3 : 233, 294, 349) ' Bb3 - D4 - F4
    r >>= 1 ' transpose one octave down
    note_cnt++
PRI waveshape(x) : r ' wave shaping using arctan transfer function
    _,r := xypol($2000,x) 
    return clamp(r sar 15)
PRI clamp(x) : r ' clamp to valid 16 bit range
    return x <# $7FFF #> -$7FFF

Something I wrote to pass an hour or so. It's a basic Karplus-Strong synth with a rudimentary tube amp simulation. It'd probably sound better if there were multiple channels and the decay of the previous note was allowed to continue. Or to play chords, of course.

Nice!
Once again cordic shines!
I am a great fan of asymmetric overdrive. So perhaps you might want to add some offset before the arctan, which will add 2nd harmonics and therefore enrich the sound in a nice way.
Also a little bit of even a very simple reverb can do much....
Christof