Author: David Adlberger

Researching Automated Mixing Strategies for Clarity and Real-Time Composition

As the Image Extender project continues to evolve from a tagging-to-sound pipeline into a dynamic, spatially aware audio compositing system, this phase focused on surveying and evaluating recent methods in automated sound mixing. My aim was to understand how existing research handles spectral masking, spatial distribution, and frequency-aware filtering—especially in scenarios where multiple unrelated sounds are combined without a human in the loop.

This blog post synthesizes findings from several key research papers and explores how their techniques may apply to our use case: a generative soundscape engine driven by object detection and Freesound API integration. The next development phase will evaluate which of these methods can be realistically adapted into the Python-based architecture.

Adaptive Filtering Through Time–Frequency Masking Detection

A compelling solution to masking was presented by Zhao and Pérez-Cota (2024), who proposed a method for adaptive equalization driven by masking analysis in both time and frequency. By calculating short-time Fourier transforms (STFT) for each track, their system identifies where overlap occurs and evaluates the masking directionality—determining whether a sound acts as a masker or a maskee over time.

These interactions are quantified into masking matrices that inform the design of parametric filters, tuned to reduce only the problematic frequency bands, while preserving the natural timbre and dynamics of the source sounds. The end result is a frequency-aware mixing approach that adapts to real masking events rather than applying static or arbitrary filtering.

Why this matters for Image Extender:
Generated mixes often feature overlapping midrange content (e.g., engine hums, rustling leaves, footsteps). By applying this masking-aware logic, the system can avoid blunt frequency cuts and instead respond intelligently to real-time spectral conflicts.

Implementation possibilities:

• STFTs: librosa.stft
• Masking matrices: pairwise multiplication and normalization (NumPy)
• EQ curves: second-order IIR filters via scipy.signal.iirfilter

“This information is then systematically used to design and apply filters… improving the clarity of the mix.”
— Zhao and Pérez-Cota (2024)

Iterative Mixing Optimization Using Psychoacoustic Metrics

Another strong candidate emerged from Liu et al. (2024), who proposed an automatic mixing system based on iterative masking minimization. Their framework evaluates masking using a perceptual model derived from PEAQ (ITU-R BS.1387) and adjusts mixing parameters—equalization, dynamic range compression, and gain—through iterative optimization.

The system’s strength lies in its objective function: it not only minimizes total masking but also seeks to balance masking contributions across tracks, ensuring that no source is disproportionately buried. The optimization process runs until a minimum is reached, using a harmony search algorithm that continuously tunes each effect’s parameters for improved spectral separation.

Why this matters for Image Extender:
This kind of global optimization is well-suited for multi-object scenes, where several detected elements contribute sounds. It supports a wide range of source content and adapts mixing decisions to preserve intelligibility across diverse sonic elements.

Implementation path:

• Masking metrics: critical band energy modeling on the Bark scale
• Optimization: scipy.optimize.differential_evolution or other derivative-free methods
• EQ and dynamics: Python wrappers (pydub, sox, or raw filter design via scipy.signal)

“Different audio effects… are applied via an iterative Harmony searching algorithm that aims to minimize the masking.”
— Liu et al. (2024)

Comparative Analysis

Both methods offer significant value. Zhao’s system is elegant in its directness—its per-pair analysis supports fine-grained filtering on demand, suitable for real-time or batch processes. Liu’s framework, while computationally heavier, offers a holistic solution that balances all tracks simultaneously, and may serve as a backend “refinement pass” after initial sound placement.

Looking Ahead

This research phase provided the theoretical and technical groundwork for the next evolution of Image Extender’s audio engine. The next development milestone will explore hybrid strategies that combine these insights:

• Implementing a masking matrix engine to detect conflicts dynamically
• Building filter generation pipelines based on frequency overlap intensity
• Testing iterative mix refinement using masking as an objective metric
• Measuring the perceived clarity improvements across varied image-driven scenes

References

Zhao, Wenhan, and Fernando Pérez-Cota. “Adaptive Filtering for Multi-Track Audio Based on Time–Frequency Masking Detection.” Signals 5, no. 4 (2024): 633–641. https://doi.org/10.3390/signals5040035:contentReference[oaicite:2]{index=2}

Liu, Xiaojing, Angeliki Mourgela, Hongwei Ai, and Joshua D. Reiss. “An Automatic Mixing Speech Enhancement System for Multi-Track Audio.” arXiv preprint arXiv:2404.17821 (2024). https://arxiv.org/abs/2404.17821:contentReference[oaicite:3]{index=3}