COSC 414 Audio in Games Digital Audio -- Part 1
Sound Something vibrates in the air creating waves of pressure on your eardrums that your brain interprets as sound. Sound pressure measured in decibels, dB. 0 dB - Threshold of hearing 10 dB - Rustling leaves 20 dB - Whisper 60 dB – Conversation 110 dB – Rock Concert 130 dB - Threshold of pain 160 dB – Instant perforation of eardrum
Sonic Elements Audio Types: Music Voice Over Dialog Sound Effects
Audio Uses: Alert Information Mood Sonic Elements
Digital vs. Analog Wave Forms- Analog = continuous Digital = discrete To convert from analog to digital: sample - Look at amplitude at regular intervals Convert to a number Use number to play back the sound.
Digital Audio Sampling 1Hz=1 Hertz = 1 cycle per second Sample rate Telephone Quality 11 KHz, 8 bit, mono Radio Quality 22 KHz, 8bit, mono CD Quality 44 KHz, 16 bit, stereo As sample rate increases ... Quality increases File size increases Fundamental Problem of Multimedia: Balance file size with asset quality
1 byte: +/- 128 discrete values 2 bytes: +/- 32767 data points 1 minute of CD quality audio 44100 samples per second X 2 bytes per sample X 2 channels X 60 seconds 10.5 Mb per minute Sampling Rates http://gwc.sourceforge.net/gwc_science/node2.html
Compression Holy Grail of Audio: Develop the best algorithm, one that combines high quality at low bitrates and works everywhere. First standard in audio compression: MPEG This algorithm was developed by the Motion Picture Experts Group (MPEG), as an International Organization for Standardization (ISO) standard for the high fidelity compression of digital audio.
Psychoacoustics How does the human audio perception influence compression? Human hearing masks weaker signals whenever the presence of a strong audio signal makes a temporal or spectral neighborhood of weaker audio signals imperceptible. “Selective Hearing” http://www.dtic.upf.edu/~xserra/cursos/TDP/referencies/Pan-Davis-IEEE-MJ-1995-MPEG-Audio-Compression.pdf
Production Values Sound Studio Professional Voices Ambiance, Decay, Echo Plan using the Storyboard Get it all in one studio session Professional Audio Editor