bass-foundry/docs/rivet/research/psychoacoustics.md

Psychoacoustics, expectation, and creative direction

The product target

Treat a heard musical gesture as the unit of composition: its trigger timing, pitch movement, articulation, timbral trajectory, placement against other parts, and relationship to what the listener has already heard. MIDI notes describe only some of those properties. A held note can contain a rising resonance, several rhythmic pulses, a change in texture, and a long answering tail.

The design proposals below are hypotheses for a creative tool. The cited experiments establish particular perceptual effects under their study conditions; they do not establish universal rules for riddim or Devath's intentions.

Research-grounded mechanisms

Expectation depends on context

Cheung et al. found an interaction between uncertainty and surprise in ratings of Western tonal chord sequences. Both an unexpected event in a predictable context and an expected event in an uncertain context could receive high pleasure ratings. This supports exploring relationships between recognition and deviation, while leaving genre, listener experience, and musical context explicit.

Cheung et al., 2019, original study abstract

Design inference: preserve an identifiable anchor while changing another property, and offer confirmation after a passage of ambiguity. A novelty score alone cannot select a meaningful continuation.

Groove involves a stable frame and rhythmic challenge

Witek et al.'s drum-break study found greatest pleasure and desire to move at intermediate syncopation levels. This was a result for their stimuli and listeners, not a genre-independent target number for a sequencer.

Witek et al., 2014

Design inference: distinguish the pulse-bearing parts from a freely moving foreground. A surprising bass or lead event can be easier to follow when drums, phrase length, or a recurring attack still provide orientation. Intentional extremes remain valid creative choices.

Timbre contributes its own tension

Farbood and Price found evidence linking greater roughness, inharmonicity, and spectral flatness to greater judged tension in their sound comparisons. Evidence for spectral centroid as a tension predictor was ambiguous. Brightness, roughness, loudness, harmonic function, and emotional meaning should remain separate concepts.

Farbood and Price, 2017

Design inference: a melodic arrival and a timbral release can happen together, independently, or in opposition. A line can keep its pitches while its texture becomes less abrasive. A quiet sound may remain harmonically unresolved.

Grouping determines which sounds form a phrase

Elhilali et al.'s human psychophysics experiments showed that relative timing can strongly affect whether tones are heard as a coherent stream. Their findings challenge an account based solely on frequency separation.

Elhilali et al., 2009

Design inference: a motif distributed between sounds needs perceptual connections. Shared timing, related articulation, recurring contour, and deliberate handoffs are candidates to test. A MIDI line split across unrelated patches may be heard as several parts rather than one melody.

Preferences are learned as well as sensory

McDermott et al. found substantial cultural variation in consonance preferences, including indifference to consonance versus dissonance in a population with little Western musical exposure. This argues against presenting Western consonance preferences as a universal measure of musical worth.

McDermott et al., 2016

Design inference: genre fluency and the producer's taste matter. Scale adherence, chord-tone density, and estimated roughness can describe an option; they should not become an automatic good/bad ranking.

Reading the supplied Devath references responsibly

The local measurements establish changes in mix level, attack activity, and broad spectral texture. For example, HENKA has a measured reduction around 2:03–2:35 and Phantasy around 1:27–2:23. Petals maintains more consistent relative activity across much of its earlier duration. These contrasts support studying both large departures/returns and development within an ongoing groove.

Those measurements do not establish what the melody is, how the harmony moves, which sound is foreground, or what emotional meaning a listener assigns. Exact note-level claims require an annotated listening pass, preferably with stems or MIDI. The existing report deliberately leaves those questions open.

For each reference passage, annotate the following rather than only naming a key:

1. Anchor: what remains recognizable—attack pattern, interval, texture, bass pulse, or a small melodic shape?
2. Foreground: which part attracts attention, and when does that change?
3. Motion: does movement come from pitch, amplitude pulses, spectral movement, articulation, spatial effects, or several at once?
4. Expectation: what seems about to happen, and what is confirmed or withheld?
5. Space: which event is absent, shorter, farther away, or easier to hear?
6. Memory: when something returns, what has changed around it?

These are listening questions, not findings already established about each file. Reference tracks supply examples of possibilities; they do not define the bounds of the producer's own style.

What the tool should let a producer do

Work on relationships

Useful requests are specific and relational:

• Keep this bass groove and let a smaller melodic answer occupy its gaps.
• Preserve the pickup; make the destination later and more exposed.
• Keep the notes but contrast short, dry articulations with a sustained answer.
• Let one timbre finish a phrase that another timbre starts.
• Keep harmonic ambiguity while reducing rhythmic activity.
• Return to a familiar gesture with softer texture and different accompaniment.
• Turn the ending into a pickup for the next loop, rather than closing it.

The original motif can survive any of these transformations. The producer chooses which relationship matters and which dimensions are free.

Separate useful descriptors

Avoid a single emotional-intensity control. Explore these dimensions separately:

Dimension	Example experiment
Pulse clarity	Keep drums fixed while moving foreground attacks.
Anticipation	Bring the pickup forward; delay the destination.
Activity	Remove connective notes while retaining signature anchors.
Articulation	Keep onset locations and compare different note lengths/tails.
Harmonic stability	Hold melody fixed over different bass/chord contexts.
Timbral tension	Keep pitches fixed while changing an explicitly mapped patch macro.
Continuity	Pass the motif between related and contrasting voices.
Familiarity	Reintroduce a recognizable fragment after a departure.

These descriptors help propose experiments. They do not measure longing, sadness, euphoria, or artistic merit. Several can point in different directions at once.

Capture how the actual sound behaves

The same MIDI onset can produce different heard attacks through different patches. A slower attack, rhythmic modulation, portamento, or a long release can change the musical role of a note. Accurate evaluation therefore needs the production sound and surrounding loop, with repeated audition rather than only an isolated tone.

A future sound profile could record an approximate attack delay, release tail, comfortable register, and user-mapped expressive controls. Audio returned from the synth could help measure those responses. A MIDI-only generator cannot infer the behavior of an arbitrary patch or automatically control its macros without an explicit routing/mapping arrangement.

Make creative moves composable

The current eight families are useful initial experiments. Further freedom comes from chaining smaller operations with a visible history:

• select and preserve an anchor;
• fragment, displace, stretch, repeat, or subtract an event group;
• choose a destination relative to the surrounding harmony;
• hand a gesture to another voice;
• change its articulation or a mapped timbral trajectory;
• bring a remembered fragment back in a new context.

A producer should be able to branch an idea, pin a particular decision, compare branches in context, and reuse a personal gesture. Multiple operations should compose without forcing every phrase into a statement/climax/resolution arc. Circular, suspended, sparse, and continuously evolving structures are valid.

Preserve learning and authorship

Three proposals should illustrate different musical hypotheses. For example:

1. same pitches, more space, a later arrival;
2. same groove, a different harmonic destination;
3. a fragment handed between two explicitly assigned voices.

Keep the surrounding loop and listening level comparable, so the producer can judge the changed relationship. Store the chosen material and the specific choices he wants to preserve. Optional explicit favorites can become a personal vocabulary; generic musical rules should remain adjustable.

Practical next research steps

1. Annotated reference sessions. Select short passages from the supplied files and mark anchors, foreground roles, handoffs, withheld events, and returns. Check claims against repeated listening instead of treating a waveform as a melodic transcription.
2. Controlled comparisons using the friend's own patches. Keep notes fixed while changing articulation; keep articulation fixed while changing rhythm; compare the same line under two harmonic settings. Check the whole loop as well as isolated examples. Avoid making the louder example automatically seem more successful.
3. A reusable gesture and branch history. Extend the current note/pin model toward saved groups with independent timing, pitch, articulation, voice, and mapped modulation choices.
4. Two-role experiments. Explore interlocking bass and answer lines before expanding into a full arranger or arbitrary multi-instrument generator.
5. Producer evaluation. Ask whether a suggestion leads to a usable section, whether he can retain its useful moment, and whether the tool keeps him in the writing flow. Test over repeated sessions; mathematical novelty is insufficient.

Current implementation boundary

Version 0.2 already covers structured note/rhythm proposals, harmony context, separate note locks, pinned sections, and external MIDI audition. It does not yet represent patch-dependent audible gestures, mapped timbral motion, multiple sound roles, reusable branch histories, or verified perceptual/emotional judgments. The next design work should make those relationships explicit while keeping the producer's listening decisions central.