Click here to see diagrams of various windowing functions.Įach window is then subjected to a form of spectral analysis called an STFT, or short-time Fourier transform. Proper windowing, along with adding some 0's to the end of the sample frame (called zero-padding), helps minimize the phenomenon of spectral leakage, whereby the energy at a particular frequency band actually spills into adjoining bands. It is well worth the effort to try each windowing function to observe the effect on your final sound. Common window shapes for phase vocoding, most being bell-shaped, are Hamming, Kaiser, Blackman and von Hann (Hanning).
#SOUNDHACK SPECTRAL GATE WINDOWS#
The shape of these windows will have an effect on the weighting of the resultant analysis, and ultimately the character of the recreated sound. The first part of the process involves dividing a digital sample input signal into numerous time segments or blocks of samples and then multiplying those blocks by an envelope called a windowing function, pictured without the often used overlaps on the left. The initial phase vocoding analysis component entails a process whereby a highly granular time domain sequence of digital samples is converted into a less granular time and also frequency band representation of sound. And (perhaps sadly) the ubiquitous modern-day auto-tune algorithm is also based upon phase vocoding technology.
#SOUNDHACK SPECTRAL GATE SOFTWARE#
Most recently as of this writing, a C/C++ library and SDK made by Zynaptiq called ZTX is at the top of the precision pitch/speed change game and is incorporated into many popular audio software titles such as MAX and Digital Performer. Miller Puckette, creator of MAX and Pd, might be credited with developing the first real-time phase vocoder. These took advantage of the much higher computational speed available at the time. More practical phase vocoders were developed in the 1970's and 80's, perhaps most notably Mark Dolson's in 1983. Unlike the classic studio technique of changing the speed of an audio tape, where time change is linked to pitch change (the slower the tape, the lower the pitch and vice versa), phase vocoding was a welcome tool for composers when it came along with the advent of digitized audio files and analysis algorithms as early as 1966 (Flanagan and Golden, Bell Labs). Often a combination of the two (alterations of both pitch and time) is used.
Other possible uses include compressing a sound in time without changing the original pitch or changing pitch without changing original time. The classic use of a phase vocoder is to stretch the original sound out in time without changing its original pitch. Unlike the similarly-named channel vocoder, due to the spectral analysis phase, pv is a purely digital technique. Our readers have come to expect excellence from our products, and they can count on us to maintain a commitment to producing rigorous and innovative information products in whatever forms the future of publishing may bring.Phase vocoding (pv) is a form of synthesis by analysis in that a digital sound file or stored buffer is analyzed and is then resynthesized by the phase vocoder. Through our commitment to new products-whether digital journals or entirely new forms of communication-we have continued to look for the most efficient and effective means to serve our readership. Since the late 1960s, we have experimented with generation after generation of electronic publishing tools. The Press's enthusiasm for innovation is reflected in our continuing exploration of this frontier.
We were among the first university presses to offer titles electronically and we continue to adopt technologies that allow us to better support the scholarly mission and disseminate our content widely. Among the largest university presses in the world, The MIT Press publishes over 200 new books each year along with 30 journals in the arts and humanities, economics, international affairs, history, political science, science and technology along with other disciplines.
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