EE2F2 - Music Technology

1. 7. Synthesis & Sampling EE2F2 - Music Technology

2. Introduction • Sounds & Timbre • What makes instruments sound different? • Electric Instruments • Guitars, pianos & organs • Synthesis • Analogue synthesis (subtractive and additive) • Digital synthesis • Sampling • Sampling techniques • Sample + Synthesis • Physical Modelling • Classic and functional modelling techniques

3. Sounds & Timbre Take a pair of simple sounds: • What makes these instruments sound different? • Pitch? • No, the pitches are identical • Volume? • No, their average power levels are identical • Waveform shape? • Nearly, although waveforms with different shapes can sound the same • Spectrum? • Yes - or, in musical terms, the timbre Flute Oboe

4. Harmonics • All periodic waveforms (e.g. sounds) are formed from a series of sine waves that have: • Frequencies of integer multiples of the fundamental frequency • Amplitudes that define the timbre • The amplitudes of the fundamental and harmonics are the spectrum of the waveform • You can predict how a waveform will sound by looking at the spectrum • Most energy concentrated in the fundamental gives pure, ‘mellow’ sounds – e.g. a flute • Lots of high frequency harmonics gives harsh, ‘raspy’ sounds – e.g. a trumpet

5. Fundamental Frequency 1st Harmonic 2nd Harmonic Examples

6. Time Variations • The timbre of many sounds develops over time. Example, a grand piano (middle C): Upper harmonics decay rapidly Lower harmonics persist

7. Pitch Variations • The weights of each harmonic often also varies with the pitch of the note played. • Example, an oboe: Spectrum Oboe, A3 0 1000 2000 3000 4000 f [Hz] Spectrum Oboe, A4 0 1000 2000 3000 4000 f [Hz] Oboe, A4, played at half speed Spectrum 0 1000 2000 3000 4000 f [Hz]

8. C#2 139 D#2 156 F#2 185 G#2 208 A#3 233 C#3 277 D#3 311 F#3 370 G#3 415 A#4 466 C2 131 D2 147 E2 165 F2 175 G2 196 A3 220 B3 247 C3 262 D3 294 E3 330 F3 349 G3 392 A4 440 B4 494 (Frequencies in Hertz) Terminology – Pitch and Frequency • The pitch of notes is perceived on a logarithmic frequency scale • In musical terms, the ‘interval’ between two notes corresponds to the ratio between their frequencies. • E.g. • Octave – A doubling of frequency • Semitone – There are 12 semitones in an octave, one semitone, therefore, corresponds to a frequency ratio of 21/12» 1.06

9. ‘Velocity’ Variations • The timbre of many instruments also varies depending how loud a note is played • In MIDI terms, this corresponds to the ‘velocity’ byte of a note-on message • Example, grand piano:

10. Sounds & Timbre – Summary • The timbre of a sound is related to the shape of the frequency spectrum • It’s what makes instruments sound different to one another • For a single instrument, timbre can vary with • Pitch • Velocity • Time • Other performance controllers • If you want to synthesise an instrument, all these factors must be simulated

11. Electrical/Electronic Instruments • Most electrical and electronic instruments emulate traditional acoustic instruments in terms of: • Sound: the listener hears an instrument that sounds like the real thing • E.g. synthesisers and samplers • Performance: the artist plays an instrument that feels and responds like the real thing • E.g. electric guitars, electric pianos • Sound and performance: the instrument sounds and feels like the real thing • E.g. Digital pianos, electronic drum kits • Neither: Novel instruments with novel sounds • E.g. Theremins, computer generated ‘unphysical’ models

12. Electric Instruments • Many early electric instruments were designed to feel like their acoustic counterparts without necessarily sounding the same • This led to the unique sounds of: • Electric guitars • Electric pianos • ‘Tone-wheel’ electric organs • All these examples rely on magnetic pick-ups (rather than acoustic microphones) for their operation

13. Magnetic Pick-ups • A vibrating string doesn’t actually displace much air so it doesn’t make very much sound • Acoustic instruments use a soundboard to amplify the vibrations • Electric instruments detect vibrations in steel strings using a magnetic pick-up and then amplify them electrically

14. Electric Guitars • Unlike an acoustic guitar, the body is solid and doesn’t amplify the string vibrations • Three sets of six pick-ups (one per string) • Controls mix together the three outputs • Also provide volume and tone (basic EQ)

15. Electric Pianos • Real pianos are HUGE • They need to be big because: • They contain over 200 strings, some over a metre long • The body of the piano amplifies the sound from these strings being struck with a hammer • Electric pianos have very similar keyboards and hammer mechanisms (so they feel the same) • The sound is produced by the hammer hitting a metal bar instead of a string • The vibrations of the bar are amplified electrically via a magnetic pick-up • It doesn’t sound like a piano, but it does feel like one

16. Inside an Electric Piano Example: Rick Wakeman, Journey to the Centre of the Earth

17. Electric Organs • Each key/pedal switches an oscillator into the mixed output. • Question: How do you keep 91 oscillators in tune?

18. Hammond Tonewheel • Solution: The tonewheel

19. Electric Instruments Today • Guitars • Still hugely popular – the defining sound of most rock bands • Electric Pianos • Overtaken by digitally sampled pianos • Most digital pianos do, however, still feature an electric piano voice • Organs • Electronic organs are still used • Mostly, they are incorporated into general purpose synthesisers • The tonewheel sound is so distinctive, however, that some modern keyboards attempt to emulate it

20. Electric Instruments - Summary • Electric instruments tend to be designed to ‘feel’ like their acoustic equivalent, but not necessarily sound like them • Most work using magnetic pick-ups • Although they don’t sound like the acoustic version, their own unique sounds have made them established instruments in their own right (especially in the case of the electric guitar) • Next time: Sound synthesis