One idea I had was to store a separate pitch for the attack and decay/sustain segments. This let me add a virtual track that sends attacks to the pulse 1, pulse 2, or triangle channel. It lets me run two sequences on one channel. Think of it as triangle drums without the drums.
Did you fail to understand the concept of attack and sustain portions, or did you fail to understand the concept of overwriting? It matters little; I'll explain both.
Attack and sustain portions
This section assumes familiarity with FamiTracker envelopes and with volume fade effects in trackers. Consider the following volume envelope:
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___ _| |___ | |___ | |_______ _| . |_______________ | . |_______________ | . . |____________ | . . | . . . . . . . . . . . . . . . . . . . . . . . . 4 7 8 8 7 7 6 6 5 3 Attack phase Sustain phase
Envelopes in my music engine are slightly more complex than this to allow for pitch and duty control, but this simplified model should help you begin to understand.
Normally the music engine has have five tracks going, each with its own position in a musical phrase:
- A standard melodic track that plays on pulse 1
- A standard melodic track that plays on pulse 2
- A standard melodic track that plays on triangle
- A track that triggers sound effects, used to create drums
- A track that can replace the attack on pulse 1, pulse 2, or triangle with a different note
Track 4 is mapped to a drum kit. Each entry in a 25-entry array consists of two sound effect numbers. Usually one sound effect is on the noise channel and the other on the triangle channel if needed. Triggering a sound effect of the form "triangle portion of kick drum" allows triangle drums to interrupt the bass line.
Track 5 doesn't have its own hardware APU channel. Instead, it has a pointer to another channel (pulse 1, pulse 2, or triangle). When a note is played on track 5, the track overwrites that other channel's attack with the attack portion of the instrument chosen for track 5. This pauses the other channel's sustain until the attack finishes.
What you're hearing in this NSF is a bass line on track 3 and an instrument with a one-frame pop attack on track 5. Track 5 is set to write attacks on top of track 3, which causes its sustain to pause until the attack is finished. Because the attack has a different pitch, tracks 3 and 5 are effectively time-sharing the triangle channel. It's the melodic counterpart to triangle drums.
- An instrument can specify "staccato", where each note is cut half a row before the note ends. Should this cut an injected attack?
- Should regular note offs cut an injected attack?
- Should a new note on an instrument with an attack of nonzero length cut an injected attack?
- An instrument can specify "legato", where a new note does not restart the envelope but only changes the current note's pitch. This is used for hammer-ons and pull-offs and wind instrument grace notes. Should legato change the pitch of an injected attack?
- If one or both tracks has arpeggio turned on, is the attack affected?
- Have legato and note cut affect the attack phase only if attack and sustain pitches match, on the assumption that a match was not an injection.
RAM: +0; composer must take care to avoid unisons
- Store a separate variable for whether an attack is injected.
RAM: +3 BSS, or +0 if attack pitch bit 7 can be repurposed for this
- Don't inject attacks at all, but instead give the attack track its own virtual channel (with base pitch, attack state, and arpeggio state) that the pulse 1, pulse 2, and triangle channels consult, similarly to how sound effects work
RAM: +2 ZP (-3 BSS for channel attack pitch; +2 ZP +1 BSS for attack track's attack state; +2 BSS for attack track's arpeggio state)
* Simple in Pently, that is. In FamiTracker, the MMC5 pulse is required unless you want to make a mess of Gxx and repeated versions of the lead's envelope offset by various numbers of frames.