Sonic Visualiser

Sonic Visualiser is a layer-based spectrographic analysis tool designed by researchers at Queen Mary University of London for academic audio analysis. Its layer system makes it exceptionally powerful for EVP work: you can stack a waveform layer, a colour spectrogram, a peak-frequency track, and text annotation notes — all time-aligned and viewable simultaneously — over a single recording.

The annotation layer is the key differentiator. When you identify a potential EVP event, you can mark the precise time range, label it with a transcript attempt, and export everything as a structured dataset or publication-quality image. For investigators who need to present findings to sceptical audiences, Sonic Visualiser produces spectrograms where the evidence can be clearly indicated on the frequency-time plot.

Sonic Visualiser also supports Vamp audio analysis plugins — a library of open-source signal processing algorithms. The Melodia pitch estimator plugin can extract a fundamental frequency track from a recording, which helps distinguish human voices (which follow musical pitch contours) from mechanical artifacts (which tend to produce fixed-frequency tones).