Phosphor gives you direct control over the frequency spectrum. Paint pads, textures, drones, risers, and evolving soundscapes by drawing them. Choose from four synthesis engines, shape dynamics with a built-in ADSR envelope, and export in multiple formats. Ready to drop straight into your DAW.
Every sound can be represented as a spectrogram, a picture where time runs left to right, frequency runs bottom to top, and brightness represents loudness. A bass note is a bright horizontal line near the bottom. A siren is a diagonal streak. A snare is a vertical column.
Phosphor inverts this: instead of turning sound into a picture, it turns a picture into sound. You paint directly onto the spectrogram, and Phosphor synthesises audio from what you've drawn.
How It Works
Paint or load an image onto the spectrogram canvas. Draw freehand, use the harmonic brush, or import any image file.
Hear it instantly. Phosphor synthesises a real-time preview as you work so you can iterate quickly.
Adjust and refine, choose your synthesis engine, shape the ADSR envelope, change frequency scale, duration, dynamic range, and toggle musical overlays like piano roll and beat grid.
Export in your choice of format and bit depth, with full iterative phase reconstruction for the final render.
Spectrogram Canvas
Draw directly on a frequency-vs-time canvas. The vertical axis follows a logarithmic scale mapped to musical octaves, so equal distances always equal musical intervals. Includes piano roll overlay, beat grid, and snap-to-note.
Colour Mode
In standard mode, brightness controls loudness and every frequency is a pure sine. In colour mode, hue shapes the timbre, red produces sawtooth-like warmth, green gives square-wave hollowness, blue creates soft flute-like tones. Saturation controls harmonic intensity.
Four Synthesis Engines
Choose how your spectrogram becomes sound. ISTFT for classic spectral synthesis with iterative phase reconstruction. Additive for clean, precise oscillator-bank synthesis. Noise Band for textural, granular results. Blend to mix tonal and noise components.
ADSR Envelope
Shape the amplitude dynamics of your sound with a full attack-decay-sustain-release envelope. Visualise the envelope shape in real time as you adjust parameters.
Image Sonification
Load any photograph, painting, fractal, or generated image. Phosphor maps the visual composition to audio, brightness to loudness through a perceptual dB curve, vertical position to pitch, horizontal position to time. Every image has a sound.
Flexible Export
Export in WAV, AIFF, FLAC, or MP3. Choose 16-bit, 24-bit, or 32-bit float at 44.1kHz or 48kHz. Optional peak normalisation. The exported audio uses iterative phase reconstruction for clean results.
Platform: macOS 12+ (Apple Silicon and Intel)
Export formats: WAV, AIFF, FLAC, MP3
Bit depth: 16-bit, 24-bit, 32-bit float
Sample rates: 44.1kHz, 48kHz
Synthesis engines: ISTFT, Additive, Noise Band, Blend
Phase reconstruction: Fast Griffin-Lim (export), random phase (preview)
Canvas scales: Logarithmic, Mel, Linear, ERB
Window types: Hann, Blackman-Harris, Hamming, Rectangular
Licence: Freeware. Free for any use, personal or commercial
Freeware: Free for any use, personal or commercial
Got Questions?
Frequently asked
questions
Phosphor started because I wanted to build the tool I'd been imagining since I first saw hidden images in Aphex Twin spectrograms. It's a personal project built on years of working with audio DSP, spectral analysis, and music production tools.
Spectral synthesis engine written in C++
Perceptual frequency mapping based on psychoacoustic research
Iterative phase reconstruction using Fast Griffin-Lim (Perraudin et al., 2013)
Resources