ListenAid

ListenAid - intuitive & clean realtime audio spectrum analysis.

ListenAid is an acoustic visualization tool optimized for live sound engineering and system tuning (leveraging transfer functions and multi-resolution processing), delivering maximum performance through Metal and Accelerate hardware acceleration.

Audio Engine & Core DSP • Lock-Free Processing (RingBuffer): non-blocking, zero-dropout audio. • Low-Level Math (vDSP): minimal CPU load • Real-Time Transfer Function: Live reference vs. live channel division: instantly shows frequency responses differences

5 different Analysis models: • STFT: Standard Short-Time Fourier Transform. • CWT: Continuous Wavelet Transform for high-frequency time resolution; optimized via integral images. • CQT: Constant-Q Transform with variable smoothing. • QTAM: Amplitude demodulation in the frequency domain. • Multi-Resolution: Concurrent Low, Mid, and High FFT windows for low-end frequency and high-end time resolution.

Metal GPU Rendering • Spectrogram is GPU-offloaded; maintains 60 FPS even at massive bin sizes • Phase Reassignment: Analyzes frame phase differences, shifts energy to exact sub-bin frequencies to sharpen visual traces • Simultaneous FFT Traces: Concurrently plots Live, Reference, and Secondary traces with customizable colors and opacities • Dynamic Viewport (ViewportMath): Continuous pan and zoom

Analytical Tools & Precision • Sub-Bin Peak Detection: Calculates precise peak frequencies using FFT phase correction or logarithmic-parabolic interpolation • Pitch Conversion (FrequencyConverter): translates frequency peaks to notes, showing cent deviations (with adjustable concert pitch) • Weighting & Tilt: A- and C-Weighting filters; adjustable display tilt • Smoothing & Averaging: Exponential, RMS, LUFS, Leq or Peak Hold averaging; psychoacoustic fractional octave smoothing (1/96 to 1 full octave).

System Tests & Signal Generation • Sine Generator: Artifact-free oscillator with amplitude fade envelopes; outputs up to the Nyquist frequency • Channel Control (SystemTestManager): Routes the generator or loop player via Normal, Solo L/R, or Phase Invert • Loop Playback: Imports and loops custom audio files to test spaces using known reference tracks

Workflow & Connectivity • Multipeer Control (MultipeerManager): fully remote-control another instance at the mixing desk (volume, mute, generator, playback) • Smart Routing: AudioEngine safely intercepts hardware changes and manages BT profiles • Preset System: Instantly save and recall all DSP and UI configurations via slots A, B, and Y.