Marcelo Cicconet

Audio Analysis Units

Audio Analysis Units are Audio Units designed to provide graphical information about audio properties in real time. Being a plug-in, an Audio Unit needs a host application. The default one, provided by Apple, is AU Lab. After installing the Apple developer tools, AU Lab can be found at the folder /Developer/Applications/Audio. An Audio Unit can be found by AU Lab if it is installed at the folder /Library/Audio/Plug-Ins/Components. You can learn how to use an Audio Unit in AU Lab by reading this tutorial.

• Tuner Unit: An implementation of two simple algorithms for Fundamental Frequency Detection, one based upon the Zero Crossing Rate of the audio signal, and the other on the Harmonic Product Spectrum. Tuner Unit also plots the normalized spectrum magnitudes up to 4410 Hz. [Download Source Code]
• Spectrum Unit: It draws the normalized spectrum magnitudes up to 22050 Hz and shows the location of the first peak of that curve which is above a threshold and whose index is greater than another threshold. [Download Source Code]
• Loudness Unit: Loudness curve, defined as the root mean square of the FFT magnitudes. The FFT is performed each chunk of 512 frames, with overlap of 256 frames. [Download Source Code]
• Cepstrum Unit: Normalized Cepstrum. The Cepstrum is defined as the square of the Fourier transform of the logarithm of the squared magnitude of the Fourier transform of the sound data. It's useful for sounds with many harmonics, like human voice or guitar strings. The first 5 bins are zero padded, for technical reasons. The frequency corresponding to the maximum value is computed. [Download Source Code]
• Correlation Unit: The autocorrelation function, as calculated via Fast Fourier Transform. The window size is of 1024 frames and a hanning window is applied to the signal. This Unit also shows the frequency corresponding to the maximum of the entries whose index is greater than that of the first zero crossing. [Download Source Code]