Rocha, ManuelPestana, Pedro Duarte2026-01-082026-01-082025Rocha, M. & Pestana, P.D. (2025). SpectroFX: Real-Time Audio Effects via Graphical Spectrogram Manipulation, Revista de Ciências da Computação, 2025, no19, pp.85-100.2182-1801http://hdl.handle.net/10400.2/20719SpectroFX turns the short-time Fourier transform (STFT) spectrogram into a band- limited canvas for real-time audio effects inside VCV Rack. The digital signal processing (DSP) pipeline is deterministic: STFT/inverse short-time Fourier transform (ISTFT) with a periodic √Hann window and 50 % overlap (𝐹𝐹𝑇 𝑠𝑖𝑧𝑒 𝑁 = 1024, hop 𝐻 = N/2), explicit 1/N IFFT scaling, and overlap-add (OLA). Magnitude operators use the Open-Source Computer Vision (OpenCV) library over a 1 × 𝐾 vector per frame—Gaussian blur, unsharp-mask sharpening, Sobel edge emphasis, emboss, mirror, gating and frequency stretch—and act only within a full-width horizontal band set in the widget. Phase is reconstructed by a dedicated engine with three non-iterative modes: RAW, phase vocoder (PV) and identity phase-locking (PV-Lock). Output conditioning applies a first-order high-pass direct current (DC) blocker and a soft limiter. The design privileges predictable cost and glitch-free operation.engSpectral processingPhase vocoderPhase lockingVCV RackReal-time audioProcessamento espectralVocoder de faseBloqueio de faseAudio em tempo realjournal article