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Task 2: Rebalancing Classical Music

Image by Port(u*o)s oder Phil Ortenau from Wikimedia Commons

Hearing aid users report several issues when listening to music, including distortion in the bass, difficulties in perceiving the full range of the music, especially high-frequency pitches, and a tendency to miss the impact of quieter parts of compositions [1].

In a pilot study conducted by the Cadenza Team, we found giving listeners sliders to allow them to rebalance different instruments in a classical music ensemble was desirable.

The following example illustrates how changing the level of one instrument can alter the listening experience. The piece consists of an ensemble of five instruments: Bass, Cello, Viola, Violin 1, and Violin 2, drawn from the EnsembleSet dataset. The first sample corresponds to the original mixture. The second sample is the original track with the Violin 1 levels increased by 6 dB while keeping the rest unchanged. The last sample demonstrates the original track with the Viola levels increased by 10 dB while keeping the rest unchanged.

Violin 1

This task could be tackled by demixing the stereo into the separate instruments, applying the requested gains and downmixing. Compared to previous demix challenges a novelty is doing this for classical music instead of pop/rock. Additional novelty could also come from a causal algorithm, if you decide to make something that works for live music. Of course there are other approaches such as end-to-end that might be adapted for the task.


Entrants will be given a piece of classical music in stereo, featuring ensembles comprising between two and five instruments. They will be asked to rebalance the instruments using target gains that we will specify. Signals will be scored objectively by HAAQI and subjectively by a listener test.


We will accept causal and non-causal systems. Non-causal systems could be used for recorded music, whereas causal systems would also work for live listening. A baseline will be provided for each case. The allowed latency for causal systems will be 5 milliseconds, that is, systems cannot look beyond 5 ms into the future.


Objective metrics

Entrants will be asked to submit musical extracts for evaluation by HAAQI or an audio quality metric we are developing. For intrusive metrics, the reference will be formed by remixing the original stems with the target gains applied to each instrument. Note, we are currently working on the metrics, and a definitive list will be published when we launch the challenge. Entrants are free to use any metric they may find useful during training as well.

Listener Test

Listeners will be presented with the rebalanced signal and asked to score its audio quality. The exact form of the test is currently being designed.


[1] A. Greasley, H. Crook, and R. Fulford, "Music listening and hearing aids: perspectives from audiologists and their patients," International Journal of Audiology, vol. 59, no. 9, pp. 694–706, 2020.