The final stage of the project focused on the integration of HRV-derived MIDI files into a digital audio workstation (Ableton Live) in order to create expressive and physiologically grounded sound textures. This process was divided into two main domains: rhythmic (drum) and melodic (spectral) layers, each mapped to specific HRV parameters.
The rhythmic component was implemented first. MIDI files generated from heart rate data were imported into dedicated drum tracks. A drum sampler loaded with the Boom Kit preset was used as the primary sound generator. This particular preset was selected based on aesthetic considerations and its extended control capabilities, which provided greater flexibility for parameter mapping.
Figure 1. Drum sampler setup with Boom Kit preset in Ableton Live.
To facilitate real-time modulation, Ableton’s stock Echo device was inserted after the drum sampler. Before the drum kit, a MIDI expression control device was placed to route MIDI CC data from the HRV-derived files to specific parameters within the effects chain.
Figure 2. Full instrument rack configuration for the rhythm layer.
Among the tested mappings, a particularly compelling result was achieved by linking SDNN values to multiple targets simultaneously—namely, the feedback amount, reverb level, and transposition of the drum sounds. RMSSD was mapped to delay time, introducing irregularities and a sense of fragmentation that enriched the rhythmic texture and highlighted moments of local instability in cardiac variability.
The second major component of the sound design involved the melodic layer, constructed using frequency-domain metrics (VLF, LF, HF). MIDI files generated from these bands were distributed across three separate tracks in Ableton Live.
The VLF data was used to control a bassline, realized through the free software synthesizer Vital. Two basic sine-wave oscillators were used, one of which was tuned an octave above the other to enhance tonal richness.
LF and HF bands were each assigned to their own melodic track, both using identical synthesis architecture. In each case, two Vital instances were grouped within an instrument rack. One synthesizer generated a sinusoidal waveform, while the other used a sawtooth.
Figure 3. Oscillator configuration in Vital synthesizer using a sine waveform.
Figure 4. Oscillator configuration in Vital synthesizer using a sawtooth waveform.
This grouping enabled the use of Ableton’s chain selector feature to blend between the two timbres. The LF and HF values were routed to dynamically modulate the balance between the oscillators, producing smooth or aggressive harmonic profiles depending on the underlying autonomic activity.
Figure 5. Instrument rack in Ableton Live with activated chain selector.
To integrate the overall sympathovagal balance, the LF/HF ratio was mapped to the chain selector controlling the morphing between the two oscillators.
Figure 6. Full instrument rack setup with MIDI expression control mapped to chain selector.
This approach allowed real-time transformation of the harmonic character in response to physiological state—ranging from calm, sine-dominated tones to sharp, sawtooth-driven textures.
