New pitch instructions

[undisbeliever]

Updated 22 November 2024

• [ ] play_pitch pppppppp O-pppppp tttttttt

  • Set PITCH register to p, wait t ticks, key-off if O set.

  • MML syntax (unsure, might conflict with PM pitch-modulation):

    • P<0..16383> [,length] (with key-off)
    • P<0..16383> [,length] & (no key-off)

  • [ ] play_noise u8 noise_frequency

  • Play noise

  • MML syntax: N<0..31> [,length]

  • MML syntax: N- disables noise

  • Noise is disabled on the next play_note instruction

  • Noise is disabled if noise_frequency is out-of-bounds (> 31).

    • The bytecode assembler will transform disable_noise to play_noise $ff
    • I might turn disable_noise into a real bytecode instruction if it is used often enough.

  • CAUTION: There is only 1 noise generator. This command will will change the noise frequency on all channels playing noise.

  • CAUTION: The instrument is used to determine the length of the noise.

    • If the instrument does not loop, the noise is played for the length of the instrument's sample.
    • If the instrument loops, the noise is played until key-off.

  • TODO: Still unsure of what to do when 2 channels want to play noise at the same time. (I will figure it out after I code the noise instruction.)

  • [ ] enable_pmod

  • Enable pitch modulation on this channel

  • MML syntax: PM (unsure, might conflict with P play pitch)

  • Only channels B to F can be pitch modulated.

  • Channels G & H cannot be pitch-modulated as it conflicts with sound-effect channel ducking.

  • CAUTION: tad-gui's Play song from cursor feature cannot accurately emulate pmod. (The rust bytecode interpreter does not emulate key-on or envelopes.)

  • [ ] disable_pmod

  • Disable pitch modulation on this channel

  • MML syntax: PM0

  • [ ] set_detune offset

  • Adds offset to the PITCH register in all play_note and portamento instructions

  • MML syntax: D <offset> (detune)

  • Three bytecode instructions:

    • set_detune_i16 - Set i16 detune offset
    • set_detune_p8 arg - Sets low byte to arg, sets high byte to 0
    • set_detune_n8 arg - Sets low byte to arg, sets high byte to 0xff

  • The bytecode module will determine which instruction to use.

  • CAUTION: detune is not disabled when the instrument is changed.

  • [ ] disable_detune

  • Disable detune

  • MML syntax: D0

  • [ ] MD <cents> MML command

  • Similar to MP vibrato, it would calculate the detune offset to use on each play-note instruction.

  • Argument is in cents (1/100th of a semitone).

[KungFuFurby]

The first piece of feedback running through my head is that there should be a way to disable noise in the middle of a note (as in, prior to key off). That is... a disable_noise instruction.

I also have a way to handle the noise generator situation between music and SFX, at least so that there is some handling to avoid conflicts:

• Three frequencies are recorded: one for the music, and two for the SFX instances. A negative frequency (like $FF, at least internally speaking, since the N/negative flag is what I'm looking at) means they're not used, since noise is five bits from 0-31.
• A fourth byte handles the NON DSP register portion for the music only. The SFX will modify one of the NON bits if it is in use.
• The frequency used is the highest priority SFX going by your system. If SFX is not using noise, then the music's noise will be used.
  • Any sound that has a lower priority while noise is being used by more than one instance will have their VxVOL values zeroed out (I'm only referring to the DSP registers, not the internal volume values) until either the noise is disabled on that voice or the SFX instance is done using the noise and the voice in question is up next priority-wise.

[undisbeliever]

I've edited the play_noise instruction to add a way to disable noise.

Any sound that has a lower priority while noise is being used by more than one instance will have their VxVOL values zeroed out

This sounds possible but also very complicated in terms of managing state. The main difficulty is determining when to restore a channel's volume when noise stops in a different channel. I'm not sure if it is worth the added complexity at the moment. I'll have to think about this after I've added the play_noise instruction to the audio-driver.

[KungFuFurby]

I was looking at _update_vol_shadow_if_required__inline (albeit this may or may not turn it into an actual subroutine call in the process) to do the job of zeroing out VxVOL instead of doing a vol + pan calculation if the voice is using noise and it fails a priority check (as well as setting a dirty voice bit), and the process may be simplified if instead of a NON bit variable the music is forced to only have one voice at a time set for using noise, and the voice ID is saved in that memory location, since then the X register can simply be set to the voice ID in question.

On the MML side of things, I think N-, even without a value, might do the trick for turning off noise on a channel. This should also automatically be done when a SFX or music instance is terminated.

For other feedback not related to the ongoing discussion...

play_pitch and the pitch modulation instructions sound alright in terms of possible conflicts in MML, because P takes a number to begin with, whereas PM has a letter as the second character.

For set_detune_offset, I'd keep it running during instrument transitions, mostly because the same thing is happening for other commands (thinking of vibrato, early release, etc.).