Month: December 2008

For Wednesday’s (12/10) quiz over spectral processing, review the previous posts on intro to spectral processing, the Fourier transform, phase vocoding, and convolution. Important Concepts The quiz is not limited to the listed items below, but these concepts will go a long way towards helping you master the important material. Intro to Spectral Processing Audio…

Convolution is a fundamental process in digital audio processing. Even if you do not specifically know that the process is happening, you know the effects of the process. Filtering, reverberation, and cross synthesis all illustrate convolution. For example, a filter convolves its impulse response (IR) with the input signal to produce filtered output. Sampling reverbs convolve…

Phase Vocoding allows for independent control of time duration and pitch.  Time Expansion/Compression with Phase Vocoding The conversion of an audio signal from the time domain to the frequency domain results in a series of frames containing bins of frequency and amplitude information. If you conceive of the FFT as producing a snapshot, a frozen picture of…

Background In 1822, Jean Babtiste Joseph, Baron de Fourier developed the theorem any periodic signal could be represented as the sum of individual sine waves. The number of sine waves needed could be infinite, and each sine wave would have its own frequency, amplitude, and initial phase. The process of calculating the frequencies present in…