speech.zone

Simon October 11, 2014

Sampling and quantisation

Is digital better than analogue? Here we discover that there are limitations when storing waveforms digitally. We learn that the consequence of sampling at a fixed rate is an upper limit on the frequencies that can be represented, called the Nyquist frequency. In addition to the limitations of sampling, storing each sample of the waveform as a […]

Filed Under: Signals Tagged With: Digital signal, video, Wavesurfer

Simon February 1, 2015

Autocorrelation for estimating F0

Most methods for estimating F0 start from autocorrelation. The idea is pretty simple: we are just looking for a repeating pattern in the waveform, which corresponds to the periodic vocal fold activity. For some waveforms, it might be possible to do that directly in the time domain, but in general that doesn’t work very well. […]

Filed Under: Signals Tagged With: spreadsheet, video

Simon October 11, 2014

A simple synthetic vowel

Using Praat, we synthesise a simple vowel-like sound, starting with a pulse train, which we pass through a filter with resonant peaks.

Filed Under: Synthesis Tagged With: Harmonics, praat, Source-filter model, Spectral envelope, video

Simon October 31, 2015

The speed of sound

At the Parque de las Ciencias in Granada, Spain there is this long tube, open at the end nearest you and closed at the far end. We can calculate the length of this tube just from the audio recording, because we know the speed of sound. Here’s the waveform of part of the recording, showing […]

Filed Under: Signals Tagged With: video, Wavesurfer

Simon October 12, 2014

Entropy: understanding the equation

The equation for entropy is very often presented in textbooks without much explanation, other than to say it has the desired properties. Here, I attempt an informal derivation of the equation starting from uniform probability distributions. A good way to think about information is in terms of sending messages. In the video, we send messages […]

Filed Under: Probability Tagged With: entropy, equations, video

Simon October 25, 2014

A super-simple speech recogniser

We make what is possibly the world’s simplest speech recognition system. It can only recognise two different words, but will help you understand the basic idea of pattern recognition using template matching. The templates are just pre-recorded words, with known labels. The features extracted are just two formant frequencies in the middle of the word, […]

Filed Under: Recognition Tagged With: Classification, equations, Wavesurfer

Simon October 30, 2015