by David Adlberger -

Product IX: Image Extender

Moving Beyond Dry Audio to Spatially Intelligent Soundscapes

My primary objective for this update was to bridge a critical perceptual gap in the system: while the previous iterations successfully mapped visual information to sonic elements with precise panning and temporal placement, the resulting audio mix remained perceptually “dry” and disconnected from the image’s implied acoustic environment. This update introduces adaptive reverberation, not as a cosmetic effect, but as a semantically grounded spatialization layer that transforms discrete sound objects into a coherent, immersive acoustic scene.

System Architecture

The existing interactive DAW interface, with its per-track volume controls, sound replacement engine, and user feedback mechanisms, was extended with a comprehensive spatial audio processing module. This module interprets the reverb parameters derived from image analysis (room detection, size estimation, material damping, and spatial width) and provides interactive control over their application.

Global Parameter State & Data Flow Integration

A crucial architectural challenge was maintaining separation between the raw audio mix (user-adjustable volume levels) and the reverb-processed version. I implemented a dual-state system with:

  • current_mix_raw: The continuously updated sum of all audio tracks with current volume slider adjustments.
  • current_mix_with_reverb: A cached, processed version with reverberation applied, recalculated only when reverb parameters change or volume sliders are adjusted with reverb enabled.

This separation preserves processing efficiency while maintaining real-time responsiveness. The system automatically pulls reverb parameters (room_size, damping, wet_level, width) from the image analysis block when available, providing image-informed defaults while allowing full manual override.

Pedalboard-Based Reverb Engine

I integrated the pedalboard audio processing library to implement professional-grade reverberation. The engine operates through a transparent conversion chain:

  1. Format Conversion: AudioSegment objects (from pydub) are converted to NumPy arrays normalized to the [-1, 1] range
  2. Pedalboard Processing: A Reverb effect instance applies parameters with real-time adjustable controls
  3. Format Restoration: Processed audio is converted back to AudioSegment while preserving sample rate and channel configuration

The implementation supports both mono and stereo processing chains, maintaining compatibility with the existing panning system.

Interactive Reverb Control Interface

A dedicated control panel was added to the DAW interface, featuring:

  • Parameter Sliders: Four continuous controls for room size, damping, wet/dry mix, and stereo width, pre-populated with image-derived values when available
  • Toggle System: Three distinct interaction modes:
    1. “🔄 Apply Reverb”: Manual application with current settings
    2. “🔇 Remove Reverb”: Return to dry mix
    3. “Reverb ON/OFF Toggle”: Single-click switching between states
  • Contextual Feedback: Display of image-based room detection status (indoor/outdoor)

Seamless Playback Integration

The playback system was redesigned to dynamically switch between dry and wet mixes:

  • Intelligent Routing: The play_mix() function automatically selects current_mix_with_reverb or current_mix_raw based on the reverb_enabled flag
  • State-Aware Processing: When volume sliders are adjusted with reverb enabled, the system automatically reapplies reverberation to the updated mix, maintaining perceptual consistency
  • Export Differentiation: Final mixes are exported with _with_reverb or _raw suffixes, providing clear version control

Design Philosophy: Transparency Over Automation

This phase reinforced a critical design principle: spatial effects should enhance rather than obscure the user’s creative decisions. Several automation approaches were considered and rejected:

  • Automatic Reverb Application: While the system could automatically apply image-derived reverb, I preserved manual activation to maintain user agency
  • Dynamic Parameter Adjustment: Real-time modification of reverb parameters during playback was technically feasible but introduced perceptual confusion
  • Per-Track Reverb: Individual reverberation for each sound object would create acoustic chaos rather than coherent space

The decision was made to implement reverb as a master bus effect, applied consistently to the entire mix after individual track processing. This approach creates a unified acoustic space that respects the visual scene’s implied environment while preserving the clarity of individual sound elements.

Technical Challenges & Solutions

State Synchronization

The most significant challenge was maintaining synchronization between the constantly updating volume-adjusted mix and the computationally expensive reverb processing. The solution was a conditional caching system: reverb is only recalculated when parameters change or when volume adjustments occur with reverb active.

Format Compatibility

Bridging the pydub-based mixing system with pedalboard‘s NumPy-based processing required careful attention to sample format conversion, channel configuration, and normalization. The implementation maintains bit-perfect round-trip conversion.

by David Adlberger -

Product VIII: Image Extender

Iterative Workflow and Feedback Mechanism

The primary objective for this update was to architect a paradigm shift from a linear generative pipeline to a nonlinear, interactive sound design environment

System Architecture & Implementation of Interactive Components

The existing pipeline, comprising image analysis (object detection, semantic tagging), importance-weighted sound search, audio processing (equalization, normalization, panoramic distribution based on visual coordinates), and temporal randomization was extended with a state-preserving session layer and an interactive control interface, implemented within the collab notebook ecosystem.

Data Structure & State Management
A critical prerequisite for interactivity was the preservation of all intermediate audio objects and their associated metadata. The system was refactored to maintain a global, mutable data structure, a list of processed_track objects. Each object encapsulates:

  • The raw audio waveform (as a NumPy array).
  • Semantic source tag (e.g., “car,” “rain”).
  • Track type (ambience base or foreground object).
  • Temporal onset and duration within the mix.
  • Panning coefficient (derived from image x-coordinate).
  • Initial target loudness (LUFS, derived from object importance scaling).

Dynamic Mixing Console Interface
A GUI panel was generated post-sonification, featuring the following interactive widgets for each processed_track:

  • Per-Track Gain Sliders: Linear potentiometers (range 0.0 to 2.0) controlling amplitude multiplication. Adjustment triggers an immediate recalculation of the output sum via a create_current_mix() function, which performs a weighted summation of all tracks based on the current slider states.
  • Play/Stop Controls: Buttons invoking a non-blocking, threaded audio playback engine (using IPython.display.Audio and threading), allowing for real-time auditioning without interface latency.

On-Demand Sound Replacement Engine
The most significant functional addition is the per-track “Search & Replace” capability. Each track’s GUI includes a dedicated search button (🔍). Its event handler executes the following algorithm:

  1. Tag Identification: Retrieves the original semantic tag from the target processed_track.
  2. Targeted Audio Retrieval: Calls a modified search_new_sound_for_tag(tag, exclude_id_list) function. This function re-executes the original search logic, including query formulation, Freesound API calls, descriptor validation (e.g., excluding excessively long or short files), and fallback strategies—while maintaining a session-specific exclusion list to avoid re-selecting previously used sounds.
  3. Consistent Processing: The newly retrieved audio file undergoes an identical processing chain as in the initial pipeline: target loudness normalization (to the original track’s LUFS target), application of the same panning coefficient, and insertion at the identical temporal position.
  4. State Update & Mix Regeneration: The new audio data replaces the old waveform in the processed_track object. The create_current_mix() function is invoked, seamlessly integrating the new sonic element while preserving all other user adjustments (e.g., volume levels of other tracks).

Integrated Feedback & Evaluation Module
To formalize user evaluation and gather data for continuous system improvement, a structured feedback panel was integrated adjacent to the mixing controls. This panel captures:

  • A subjective 5-point Likert scale rating.
  • Unstructured textual feedback.
  • Automated attachment of complete session metadata (input image description, derived tags, importance values, processing parameters, and the final processed_track list).
    This design explicitly closes the feedback loop, treating each user interaction as a potential training or validation datum for future algorithmic refinements.
  • Automated sending of the feedback via email