This tool is based on a representation of a sound produced by an instrument as a modified with effects sum of some sound waves. If so, to define an instrument means to define these sound waves (called partials) and these effects (and, also, a technical constant for amplitude normalization). The following table summarizes what are arguments that are needed to create an instrument:
| Parameter | Description | Required |
|---|---|---|
| partials | List of partials (see below how they are defined) | Yes |
| amplitude_scaling | Float number that allows adjusting amplitudes over instruments; it might be set to 1 and then increased if the instrument is softer than other instruments, or decreased if the instrument is louder than other instruments | Yes |
| effects | Effects (e.g., overdrive) that are always applied to sum of partials | No |
Each partial depends on these arguments:
| Parameter | Description | Required |
|---|---|---|
| wave | Definition of wave that forms the partial (see below for more details) | Yes |
| frequency_ratio | Ratio of this partial's frequency to fundamental frequency | Yes |
| amplitude_ratio | Declared ratio of this partial's peak amplitude to peak amplitude of the fundamental (both at maximum velocity); actual amplitude ratio may be different if effects applied to the partial and to the fundamental are not the same | Yes |
| event_to_amplitude_factor_fn | Function that maps event to its multiplicative contribution to partial's amplitude; for example, this function can define dependence of amplitude on velocity (i.e., so called velocity sensing) | No |
| random_detuning_range | Range of random detuning (in semitones); this argument can be useful, because if it is more than 0, a note played for the second time sounds not exactly like for the first time | No |
| detuning_to_amplitude | Mapping from additional detuning size (in semitones) to amplitude factor of a wave with the corresponding detuned frequency; there is a sum of detuned waves instead of a single wave if this argument is provided | No |
| effects | Effects (e.g., overdrive) that are always applied to this partial | No |
Further, each wave has these parameters:
| Parameter | Description | Required |
|---|---|---|
| waveform | Form of wave; one of 'sine', 'sawtooth', 'square', 'triangle', 'pulse_10', 'pulse_20', 'pulse_30', 'pulse_40', 'white_noise', 'pink_noise', 'brown_noise', and 'karplus_strong' | Yes |
| amplitude_envelope_fn | Function that takes parameters such as duration, velocity, and frame rate as inputs and returns amplitude envelope of output wave | Yes |
| phase | Phase shift of a wave (in radians) | No |
| amplitude_modulator | Parameters of a wave that modulates amplitude of original wave (see below) | No |
| phase_modulator | Parameters of a wave that modulates phase of original wave (see below) | No |
| quasiperiodic_bandwidth | Bandwidth (in semitones) of instantaneous frequency aperiodic changes; these changes make output wave quasi-periodic and, hence, more natural | No |
| quasiperiodic_breakpoints_frequency | Expected frequency (in Hz) of random placing of time moments associated with aperiodic changes of instantaneous frequency | No |
Finally, a modulator is defined by these arguments:
| Parameter | Description | Required |
|---|---|---|
| waveform | Form of wave; one of 'sine', 'sawtooth', 'square', 'triangle', 'pulse_10', 'pulse_20', 'pulse_30', 'pulse_40', 'white_noise', 'pink_noise', 'brown_noise', and 'karplus_strong' | Yes |
| frequency_ratio_numerator | Numerator in ratio of modulating wave frequency to that of a modulated wave | Yes |
| frequency_ratio_denominator | Denominator in ratio of modulating wave frequency to that of a modulated wave | Yes |
| modulation_index_envelope_fn | Function that takes parameters such as duration, velocity, and frame rate as inputs and returns amplitude envelope of modulating wave | Yes |
| phase | Phase shift of a wave (in radians) | No |
| use_ring_modulation | Boolean indicator whether to use ring modulation instead of classical amplitude modulation; this field affects nothing if it is set for phase modulator | No |
All listed above parameters must be set inside a YAML file of particular structure. Look at an example of such file to see how it can be done.