Synthetic Audio

EE 225D, Section I: Broad backgroundSynthesis/vocoding history (chaps 2&3)Recognition history (chap 4)Machine recognition basics (chap 5)Human recognition basics (chap 18)

1Synthetic AudioA Brief Historical Introduction2Generating soundsSynthesis can be additive or subtractiveAdditive means combining components (e.g., sinusoids)Subtractive means filteredAnalogy to physical mechanismsThe human speech example 3

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Von Kempelens chess-playing automaton (~1770)6

Wheatstone speaking machine, 1837 (after von Kempelen, ~1780)7Wheatstones Speaking Machine(from von Kempelen)Vibrating reed to simulate vocal cordsNasal passageBellows for producing pressureLeather vocal tractWhistles for s and sh sounds8

Rieszs speaking machine (1930s)The Voice Operation Demonstrator (Voder)Shown at New York Worlds Fair, 1939; also San Francisco Exhibition, 1939Apparently the first electronic synthesizerRequired a human operator, long trainingRelated to human voice production, but not a physical model (no tongue analogy, etc.)Used filters to model the effect of varying vocal tract shape10(Extremely) Simplified Model of Speech ProductionPeriodicsourceNoisesourceFiltersvoicedunvoicedCouplingSpeechWhat does the spectrum of a periodic source look like?11

Voder controls

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The Voder at the 1939 Worlds Fair in New York15

DaisyVODER EXAMPLESExtended demo

16Excitations for speech soundsPeriodic: vowels, glides, liquidsNoise: voiceless fricatives (f,s)Both: voiced fricatives (v,z)Burst-like sounds: p-b,k-g,t-d17

Lesson 1 of the voder instructionsLater Speech Synthesis methods Phonemic Synth by rule: 1961 Cascaded resonances (Fant, 1953) Parallel resonances (Holmes, 1973)(synth followed by natural) KlattTalk -> DECTalk (1970s) Speak & Spell (1979) Concatenation (unit selection) The newest: HMM synthesis More on synthesis later in course

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The Klatt synthesizer, later implemented for DEC as DECtalkSpeech frequency componentsCNMAT site

21Music MachinesBarrel organs (water or spring powered)Like music boxes, pins pluck or depress keysMelography (18th century) - writable mediumPunched cards, as in Jacquard loomPlayer pianos -> modern digital versions (Bosendorfer)Telharmonium - additive sinusoidal synthesis Lots of 1900 generators = one huge machine

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17th century drawing of a water-powered barrel organElectronic musicTheramin - player varies capacitances, alters frequency and amplitude for sinusoidAnalog synthesizers - oscillators, mixers, etc. - Moog, later FM synthesisDigital synthesizers - the modern way24

Clara Rockmore at the theremin

Lon Theremin (originally Lev Sergeyevich Termen) at his instrument

26Common electronic waveformsCNMAT site

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