~DEVELOPING A CHROMATIC INTERFACE FOR
REAL-TIME DIGITAL HARMONISATION OF
SAXOPHONE PERFORMANCE
James Savage
Faculty of VCA and MCM
The University of Melbourne
[email protected]
ABSTRACT
A new interface for musical expression, the Harmonic
Table Pitch Shifter (HTPS) is presented. It is a
harmonisation system that allows free selection of
intervallic voicings to harmonise live saxophone
performance in real-time, resulting in homophonic
harmony in up to five-parts. Pitch-shifting software
developed in Max/MSP reacts to MIDI messages to
produce the desired harmonisation and features an
envelope-based mixer to give the added voices a
dynamic contour over time. A custom MIDI footpedal
based on the isomorphic note arrangement known as the
'harmonic table' places the most consonant intervals
nearest one another and also exhibits transpositional
invariance, allowing chordal 'shapes' to be freely
moved within the array without affecting their
intervallic relationship. Microswitches mounted on the
saxophone thumb rest give quick access to a piano
pedal-like effect allowing drones or chords to be
sustained beneath melodic playing or improvisation.
1. INTRODUCTION
My experience playing the guitar, piano and as an
orchestrator in the jazz idiom deeply ingrained in me the
notion that two notes in harmony are somehow greater
than the sum of their parts, but the aforementioned
musical outlets have never rewarded me with the feeling
of expressive freedom I experience when improvising
on the saxophone. In my capacity as a single-line
instrumentalist, a continuing desire to produce harmony
leads me to experiment with technology as an extension
of my saxophone playing.
Sound-on-sound looping, for example, allows
me to slowly create harmonised passages through a
process of layering. Pitch-shifters and diatonic
harmonisers deliver a means of producing harmony in
real-time, and to a reasonable extent offer real-time
control over density, dynamics and timbre. In this case
the quality has to be predetermined - a simple pitchshifter will only produce a fixed-interval voicing, and a
diatonic harmoniser will only produce consonant
harmony within a particular key centre.
The aim of this research is to develop a
chromatic interface for real-time harmonisation, and this
paper will detail the process behind the development of
one possible solution, the 'Harmonic Table Pitch
Shifter' (HTPS), which consists of a custom MIDI
footpedal and pitch-shifting audio plugin. It was
important for the control hardware to be reliable in live
performance, have a logical and easily navigable layout
and allow a wide range of chord voicings to be selected
with one or two feet. The processed audio output was to
be capable of blending with the live instrument
performance or contrasting as a distinct voice. Through
a process of experimentation, improvisation and
composition I offer conclusions regarding the viability,
potential and limitations inherent to this approach.
In the context of this research, the term
'chromatic' is used to indicate that the harmonisation
capabilities should allow the performer to produce all
possible voicings (limited only by range and number of
voices), irrespective of their degree of consonance or
dissonance. While extended saxophone techniques such
as multiphonics allow a performer to produce multiple
pitches at once, this research is limited to digital
techniques for producing harmony based on twelve-tone
equal temperament. The word 'harmonisation' is used
throughout the paper to encompass all instances where
multiple notes are sounded at once, including unisons
and octaves. The harmonisation discussed is usually
homophonic in nature, but in certain instances
incorporating horizontal displacement or independent
movement of parts I describe the effect produced as
being polyphonic.
2. PITCH SHIFTERS AND HARMONISERS
2.1. Commercially available products
Digital pitch shifters have been commercially available
since 1972, when Lexicon released their speech
pathology-focussed 'Varispeech' processor [1]. Another
early harmoniser was Eventide's H910 unit, released in
1975 - possibly the first device marketed specifically for
creating "musical harmonies" [2]. Harmonisation
products can be grouped into three main categories, with
some fitting into more than one category, depending on
their feature sets.
The simplest variety is the fixed-voicing pitch
shifter. It is capable of producing one or more additional
voices shifted at fixed intervals with respect to a live
input signal, resulting in a static voicing. These kinds of
devices generally limit the performer to utilising a single
interval type or voicing at a time, making it impossible
control harmonised voices on-the-fly while performing.
Contemporary examples usually include features from
321 2013 ICMC
