Chapter 22. Meeting 22, Discussion and Workshop22.1. Announcements• Sonic System Project Report due Thursday, 3 December • Quiz this Thursday • Download fresh martingale now: http://code.google.com/p/martingale• Download this audio file: http://bit.ly/7ZkobO22.2. Listening: Ariza• An exploration in rhythm, time, and texture • Christopher Ariza: onomatopoeticized22.3. The Vocoder: Concept• Extending the concept of envelope following • Analyze a signal with a narrow-band filter • Smooth the energy in that filter to get a control signal proportional to the amplitude (envelope following)• Use that control signal as an envelope • Use the envelope to shape a simple sound source (sine or noise) at the analysis frequency • Can remap energy from one frequency range to another 50222.4. The Vocoder: History• 1928: invented at Bell Labs by Homer Dudley • 1935: Vocoder patented • 1940s: SIGSALY (secure speech communication) system used Dudley’s vocoder Voice signal first vocoded into 10 bands to reduce information, then encrypted Image: Public domain, U.S. NSA. • 1977: EMS Vocoder 3000 16 bands each with independent level control 503© Electronic Music Studios. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse. • 1979: Moog 16 channel Vocoder released 16 bands from 50 to 5080 Hz © Moog. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse. • 1978-1982: Korg VC-10 Vocoder 20 bands 504© Korg. All rights reserved.This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.• 1980s: robot voices, Transformers (Soundwave), Cylons (Battlestar Galactica), et cetera • Soundwave (the original)505Image removed due to copyright restrictions. "Soundwave" Transformers toy. YouTube (http://youtube.com/watch?v=OWb43IB3W-c)22.5. Workshop: A Vocoder: Envelope Following• Smoothing a bipolar signal by taking the absolute value and low-pass filtering into a control signal; apply this control signal to the amplitude of pink noise 50622.6. Workshop: A Vocoder: Controlling Band-Filtered Noise• Applying the control signal to band-pass filtered white noise 50722.7. Workshop: A Vocoder: Analyzing and Generating a Signal• A narrow frequency region is analyzed with a band-pass filter; filtered noise, tuned to the same frequency, is used for generation 50822.8. Workshop: A Vocoder: Sine Wave Generation• Instead of filtered noise, the generated sound can be a sine tone tuned to the same frequency 50922.9. Workshop: A Vocoder: Two Bands with Sine Wave Generation• Tune simultaneous bands to different frequencies; mix on output 51022.10. Workshop: A Vocoder: Four Bands• Tuning for four simultaneous bands 51122.11. Workshop: A Vocoder: Eight Bands• Eight simultaneous bands with automatic frequency value generation 512• Connecting different analysis envelopes to different generation signals permits creative remapping of spectral energy 513MIT OpenCourseWare http://ocw.mit.edu 21M.380 Music and Technology (Contemporary History and Aesthetics) Fall 2009 For information about citing these materials or our Terms of Use, visit:
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