Physics 1251 The Science and Technology of Musical Sound Unit 4 Session 42 MWF Computer Music Unit 4 Session 42 MWF Computer Music

Physics 1251Unit 4 Session 41 Computer Music Please react to the following comment: “the use of computers stifles musical creativity.”

Physics 1251Unit 4 Session 41 Computer Music 1′ Lecture: MIDI provides a means for a computer to control several musical instruments in an interactive way. MIDI provides a means for a computer to control several musical instruments in an interactive way. Software is available that permits notation and composition editing. Software is available that permits notation and composition editing. Modern microelectronic is fast enough to permit real time digital signal processing. Modern microelectronic is fast enough to permit real time digital signal processing. Transmission of digital audio data requires compression schemes such as MP-3. Transmission of digital audio data requires compression schemes such as MP-3.

Physics 1251Unit 4 Session 41 Computer Music “A passion for music and a desire to push its boundaries are recurring themes at the Computer Music Center.” David Jameson Manager, Computer Music Center IBM Watson Research Center Lamentation for Jerusalem For solo Saxophone and DMIX By Daniel V. Oppenheim

Physics 1251Unit 4 Session 41 Computer Music Interactive MIDI permit novel sounds and a rich tonal palette. Microtonal Music (scales not tuned in half steps) are facilitated by computer and MIDI sequencers. Cf: Cf:

Physics 1251Unit 4 Session 41 Computer Music Software Music editors assist manuscript production and editing.

Physics 1251Unit 4 Session 41 Computer Music Demonstration: Finale 2002 ©2001 Coda Music Technology, Inc.

Physics 1251Unit 4 Session 41 Computer Music Sound Cards are the “ears” and “voices” of the minicomputer. Speaker jacks Mic jack ADC DAC

Physics 1251Unit 4 Session 41 Computer Music Microelectronics is now fast enough to permit real time digital signal processing (DSP). 80/20 Dolby Noise Reduction: A noise reduction technique in which the gain of the system automatically changes to maximize the signal-to-noise S/N ratio.

Physics 1251Unit 4 Session 41 Computer Music Signal Processing--Dolby TM Ray Dolby Founder Dolby Digital Dolby Noise Reduction Scheme: (1)During loud portions music masks noise; S/N large. (2) During soft potions increase gain to record with larger S/N. (3) Playback with appropriate gain. S/N is better than before.

Physics 1251Unit 4 Session 41 Computer Music Digital Signal Processing (DSP): 80/20 Fast Fourier Transform (FFT) An efficient algorithm (method of doing arithmetic) in which a waveform is changed into its vibration recipe. Advantages: Reduction in data set size Reduction in data set size Opportunity for processing Opportunity for processing

Physics 1251Unit 4 Session 41 Computer Music Fourier Transform Waveform Vibration (harmonic) Recipe FFT

Physics 1251Unit 4 Session 41 Computer Music Digital Filters Filters are arithmetic operators that increase or decrease the amplitude of the frequency components in the frequency spectrum (vibration recipe). Original Frequency Spectrum Low Pass Filter Processed Spectrum Frequency Noise reduced

Physics 1251Unit 4 Session 41 Computer Music Data Compression and MP-3 Bit rate = word length x baud rate Bit rate = word length x baud rate Bit rate for CD = 32 bit x 44.1 kHz > 1.4 MHz Bit rate for CD = 32 bit x 44.1 kHz > 1.4 MHz Storage requirements for 60 minutes of CD audio > 5 Gigabits. Storage requirements for 60 minutes of CD audio > 5 Gigabits. To “down load” CD over modem line (~28 kbits/sec) requires nearly an hour per minute of audio! To “down load” CD over modem line (~28 kbits/sec) requires nearly an hour per minute of audio! Need data Compression. Need data Compression.

Physics 1251Unit 4 Session 41 Computer Music 80/20 Audio Data Compression: The technique of representing the essential information required to reconstruct an audio signal from an abbreviated or compressed data set.

Physics 1251Unit 4 Session 41 Computer Music MP-3 Based on MPEG (Motion Picture Experts Group) protocols. Based on MPEG (Motion Picture Experts Group) protocols. Is a three layer compression scheme. Is a three layer compression scheme. Uses knowledge from psycho-acoustics. Uses knowledge from psycho-acoustics. The data send is 10x t0 14x compressed. The data send is 10x t0 14x compressed. The reconstructed audio file is not identical to the original, yet sounds indistinguishable from the original. The reconstructed audio file is not identical to the original, yet sounds indistinguishable from the original.

Physics 1251Unit 4 Session 41 Computer Music MP-3 Scheme FFT Buffer FilterBank MP-3 (1) Transformed (2) Masked (3) Huffman coded

Physics 1251Unit 4 Session 41 Computer Music Masking Filter Relies on psychoacoustic phenomenon of masking. Relies on psychoacoustic phenomenon of masking. Masking: a louder sound makes a simultaneous softer nearby frequency inaudible. Masking: a louder sound makes a simultaneous softer nearby frequency inaudible. Concept: if frequency is inaudible, eliminate it with digital filter. Concept: if frequency is inaudible, eliminate it with digital filter.

Physics 1251Unit 4 Session 41 Computer Music Masking Filter LOG(Amplitude) LOG(Frequency)

Physics 1251Unit 4 Session 41 Computer Music Summary: MIDI permits computer control of electronic instruments. MIDI permits computer control of electronic instruments. Music Editor software aids the composer/arranger and can even “compose.” Music Editor software aids the composer/arranger and can even “compose.” DSP manipulates digital data using binary arithmetic. DSP manipulates digital data using binary arithmetic. MP-3 compresses the audio signal information. MP-3 compresses the audio signal information.