IMGD1001 The Game Development Process Game Audio Content

IMGD-1001 The Game Development Process Game Audio (Content by professor Brian Moriarty)

Sound Audible vibration in an elastic medium (usually air)

Compression (positive pressure) Rarefaction (negative pressure)

Amount of pressure change = Amplitude Varies continuously over time

Rate of vibration/pressure change = Frequency Measured in cycles per second (Hertz or Hz)

Frequency range of human hearing: Approximately 20 to 20, 000 Hz

Analog recording and playback Transducers: Convert one type of energy to another All transducers introduce distortion

Digital audio n n n Experimental recordings: Late ‘ 60 s Jazz/classical: Early 70 s First symphonic recording: 1976 First major label recording: 1979 n Ry Cooder’s Bop Till You Drop Compact Disc n Jointly created by Sony/Phillips n Introduced October 1, 1982 n n Billy Joel’s 52 nd Street Biggest seller

Digital audio based on sampling Amplitude of signal is measured (and usually recorded) at precise time intervals, converted to stream of numbers

Digital recording and playback Extremely accurate, low noise and distortion Almost immeasurable wow or flutter Easily edited and manipulated Essentially perfect replication

Digital sampling (“digitizing”) n Sample rate Number of samples taken per second n Also measured in Hertz n n Sample resolution Range of numbers used to describe each sample n Measured in binary bits n 8 bits = 256 values (± 127) n 16 bits = 65, 536 values (± 32 K) n 24 bits = 16, 777, 216 values n

How often to sample? n Depends on desired frequency range Nyquist frequency = Sample rate required to fully express a signal n 2 X maximum required frequency n 2 X 20 k. Hz = 40 k. Hz minimum sample rate to represent full human range n

How much to sample? Depends on desired dynamic range n Dynamic range = Difference between softest and loudest sounds n Measured in decibels (d. B); 1 d. B = faintest perceptible sound n Real-world range: 10 -20 d. B (anechoic chamber) to 140 d. B (beside jet engine) n

Home audio formats n Compact Disc Sample rate: 44. 1 k. Hz n Sample resolution: 16 bits n Dynamic range: >90 d. B n Two channels for stereo n “CD quality” n n HD/Blu. Ray DVD Up to 8 channels 96 k. Hz 24 -bit audio n Dynamic range: >120 d. B n

“CD quality” data rate 44, 100 samples per second n 16 bits (2 bytes) per sample n 2 channels n 44, 100 x 2 = 176, 400 bytes/sec or 10. 584 MB per minute n Typical pop song 30 -40 MB if uncompressed n

Compressed digital audio n Lossless compression Preserves data perfectly n Compression ratio: 2: 1 typical n n Lossy compression Discards some data to increase compression ratio n The trick is: What to throw away? n

The game changer: MP 3 (1994) n Lossy compression algorithm based on auditory masking Loud low-frequency sounds can make softer high-frequency sounds inaudible n Perceptual coding: Throw away high frequencies that “can’t be heard anyway” n Compression ratio: 10: 1 or better n Pop song becomes a 3 MB file n

The MP 3 Phenomenon First Web appearance: Late ‘ 94 n Winamp, mp 3. com (Summer ’ 97) n First portable players (Spring ’ 98) n n n 32 MB Eiger MPMan F 10, Rio PMP 300 Napster (June ‘ 99)

Game audio: Early days Apple II and PC: Click the speaker n Atari, C 64, early consoles: FM synths n Macintosh (January 1984) n Ad. Lib PC sound card (1976) n Creative Labs Sound Blaster (1989) n n Ad. Lib with digital audio + game port

Game audio: Today n All game audio is digital n n Music, SFX, VO delivered prerendered Typical assets. wav (bigger, no decoding) n. mp 3 (small, decoded, may require license because of patent) n. ogg (small, decoded, no license) n. flac (smaller, decoded) n n Real-time mixing, effects,