Physical Instruments

Three instruments in bahn are physical models rather than samples or oscillators: Piano, Guitar and Violin. Each one simulates strings, a resonant body and the thing that sets the strings moving — a hammer, a pick or a bow.

That has two consequences you will notice immediately. Every control changes the instrument rather than filtering its output, so a hard pluck is brighter because the string bends further and not because a filter opened. And you can move any control while a note is sounding without a click, including Scale, which resizes the whole instrument.

What Scale does

Scale resizes the instrument. It moves three things together:

• Stiffness falls as the instrument grows. A longer string is less dominated by its own bending, which is why a concert grand sounds purer than a spinet and a dreadnought purer than a parlor guitar.
• Ring time lengthens. More string means more stored energy.
• The body's resonances fall. A bigger box resonates lower.

Scale never changes pitch. A bigger piano is not a lower piano — it is a piano whose strings are longer at the same tuning. If you want a lower instrument, write lower notes.

You can sweep it or throw it across its full range mid-note. Neither clicks.

Piano

An 88-key compass of stiff strings in unison groups over a soundboard. It plays any note the tracker sends; only the physics is fitted to MIDI 21–108, so a note outside that range still sounds at the pitch you asked for.

Maximum: 12 voices of 3 strings, 48 partials each.

Node parameters

Lane parameters

The pedal is not optional bookkeeping. A tracker row carries no key release, so without the pedal control a note has a damper resting on it and rings about half as long. Put the pedal down for a sustained passage.

Guitar

Six strings by default, each carrying one note at a time. The compass reaches down to B1 so seven-string and baritone tunings work.

Maximum: 7 voices of 1 string, 64 partials each.

One note per string

This is the part that makes it play like a guitar rather than a keyboard. A string carries one note. Play a second note on the same string and the first one stops, because the finger that stops the new note is on the same wire.

The instrument picks the string for you: the highest-pitched one that can reach the note, then downward if that string is busy. Use the String lane parameter when you want to choose — a chord voicing is a decision about where on the neck you are playing, and the automatic rule cannot know your intent.

Tunings

The seven-string table sounds seven strings. The others sound six.

Node parameters

Lane parameters

Sympathy is worth finding. Pluck one string and the others start to ring, because the bridge carries energy between them. It is most of what separates this from a sampled guitar. It is filtered by pitch agreement, so a chord thickens rather than turning to mush — and a string you have muted takes nothing.

Violin

Four strings — G3, D4, A4, E5 — driven by a bow, not by a pluck. The bow is a continuous stick-slip friction loop, so a note does not decay while you are bowing it.

Maximum: 4 voices of 1 string, 64 partials each.

The bow is three per-row controls

A bow stroke belongs to a note, so the bow's controls are lane parameters rather than node parameters. You write them per row, and you can change them mid-note to swell, lean in or lift.

BowSpeed at zero is how you end a note. A tracker row carries no key release, and a bowed note never decays on its own, so without this a note runs forever. NOTE_OFF also works and stops everything at once.

BowForce is relative, not absolute. The pressure that makes a note speak depends on how fast you are bowing and how close to the bridge you are, so this control is a multiple of whatever is right for the current speed and position. The middle of its range plays. Below it the tone thins toward a surface sound; above it the bow holds the string so hard it cannot break away and the note chokes. Both of those are sounds players use.

Node parameters

Vibrato costs nothing here. It moves the pitch and leaves the level alone, which is a property of how the strings are modelled rather than something the instrument works to achieve.

Three things these models do not claim

1. The body tables are partly measured and partly plausible. The violin's five signature modes and the guitar's three coupled low resonances come from published measurements. The higher modes in both are a generic upper body with no source behind them.
2. The bow uses a velocity-dependent friction curve. It is not the thermal friction model, which is better physics and would need measurements this project does not have.
3. Scale is not a size simulator. It moves three quantities together. It does not model a different instrument's plate thickness, bracing or varnish.

Quality under load

These instruments simplify rather than stutter when the machine is busy. See Audio Engine → Render quality under load for what that changes and what it never changes.