HarpStrata

A library for generating a layered representation of various harmonica layouts played in various positions

Overview

A harp strata represents the various interactions possible on each hole on the face of a harmonica. The interactions which are possible as well as the note which is played is governed by the harmonica layout and key, and the role that note plays in the scale range depends on this position the harmonica is being played in.

Example

||hole1|hole2|hole3|hole4| |---|---|---|---|---| |overblow|b3|-|-|b3| |blow|1|3|5|1| |draw|2|5|7|2| |single bend|b2|b5|b7|b2| |double bend|-|4|6|-| |triple bend|-|-|b6|-|

The matrix at the centre of this table is analogous to one of the representations being discussed. Each hole has multiple possible interactions, and each possible interaction will yield a particular scale degree note.

This matrix represents the first 4 holes of a major diatonic harmonica being played in first position.

HarpMatrix contract

The assumptions which will hold of all layouts presented from this library are the following:

• Elements at position [0, x] represent the interactions with the first hole on the harmonica
• Elements in the array to the right of the 0 column represent interactions with the holes sequentially to the right
• There is in principle no restriction on the number of holes which might be presented
• Any undefined values in the matrix represents interactions with holes which are not possible (for instance, a triple bend on hole 1 of a traditional major diatonic harmonica)

Key concepts

Apparatus

The Apparatus is the physical harp which is being represented. The relative pitch relationships as well as the types of bends which are availble on each hole is governed by the Apparatus you are using.

Interaction

Interaction is the name given to the way in which you get various pitches from a single hole. All holes have at least a blow and a draw Interaction. Others have bends of various kinds. Each of these has a name.

Pozition

The Pozition the harp is played in effects the location of the root note of the harp and therefore the role that any Interaction has.

Pozition is a deliberate misspelling of the word "position". This is the result of "Position" being a reserved word in Typescript. From this point on, the word "pozition" will always be spelled with a "z".

Pitch

Pitch represents the tone which is produced at each hole interaction. It is also used to identify what key a harmonica is in. This simply refers to the Pitch which is at the first position root degree.

IsActive

Represents whether the given position in the matrix is considered active or not. Making holes active / inactive represents whether they are important for the current view on the harp. The consuming library will benefit from highlighting the active ones. For example, a user considering a major pentatonic scale will want to only see the relevant holes highlighted.

HarpStrata

A composition of all of the above concepts representing a particular harp being viewed in a particular way. All of the input variables are also included in the HarpStrata so that we know how to produce the same HarpStrata again.

API

getHarps() => ApparatusIds[]

Returns an array of id's of the various Apparatus objects which can be represented with HarpStrata. The id from which can be fed in to the getHarpStrata next.

getPitchIds(?PitchIds) => PitchIds[]

Returns an array of id's of the complete list of PitchIds which exist in an octave. The id from which can be fed in to the getHarpStrata next. A PitchIds parameter can optionally be provided to indicate what the origin id of the list should be.

getPozitionIds(?PozitionIds) => PozitionIds[]

Returns an array of id's of the complete list of PozitionIds which can be taken on a harp. The id from which can be fed in to the getHarpStrata next. A PozitionIds parameter can optionally be provided to indicate what the origin id of the list should be.

getCovariantSet(CovariantControllers) => CovariantSet

Returns the complete set of covariant members given any 2 of the set. The covariant members are harp key, pozition & root pitch. Given any two of these the third can be deduced.

getHarpStrata(HarpStrataProps) => HarpStrata

Requires an ApparatusIds id object as well as a PozitionIds, PitchIds and ActiveIds object from which to deduce the DegreeMatrix, PitchMatrix and IsActiveComplex components of the returned HarpStrata.