1. Interactive Multimedia Sound Mikael Fernström

2. Data sources Microphones and transducers –Sample acoustic reality Synthesis –Simulate reality (and beyond ;-) –Many different forms of synthesis, e.g. additive, subtractive, FM, FOF, PM… Algorithms –e.g. auralisation/sonification

3. Primary processing Recording –Get clear recordings! –Signal-to-noise ratio –Acoustics Filtering –Supressing or emphasizing parts of the spectrum Mixing –Blending of several sounds sources, foreground, background, speech, music, f/x

4. Sampling “So called” CD quality –16 bit, 44.1 kHz –=> 90 dB dynamic range –Does not match normal human perception! Current professional standards –24 bit, 96 kHz –=> 138 dB dynamic range

5. Sampling… 8 bit sounds crackling, noisy Sample rates lower than 44.1 kHz, loss of treble Example: –Lowest standard encoding for human speech approx 6 bits 5 kHz (sounds like bad CB radio)

6. Quantisation

7. Simple sine wave

8. Spectrum of sine

9. Noise spectrum

10. Aliasing sound FFT

11. Aliasing Half of the FFT array gets reflected into the other half of the array

12. Hearing threshold

13. Masking

14. Formats Common formats: –WAV, AIFF, RAW… –Stores data “as is” Masking is used in perceptual compression, e.g. MP3, AAC, etc… MP3 is not MPEG! –It’s Layer 3 of MPEG-1 standard

15. Streaming Download complete file before playing Start playing file when length of file is sufficient to accommodate rest of download Start playing when length of buffer matches data rate

16. Streaming

17. MIDI Musical Instrument Digital Interface Only contains control info, no sound! –e.g. note-on, note-off, velocity/loudness

18. MIDI Sounds different depending on User synth, mapping, etc. General MIDI “standard”, GM Lack of expression, only 7 bit Sometimes problems with latency, 32.5 kb/s –Playing 10 notes simultaneously => 9.2 ms