Bandwidth : how many bits to record that sound... how many bits : * http://en.wikipedia.org/wiki/List_of_device_bandwidths * http://en.wikipedia.org/wiki/Binary_prefixes which is based on * http://en.wikipedia.org/wiki/Psychoacoustic_model Human hearing: 20Hz ... 20kHz, with resolution ~ 2Hz "CD quality" : bandwidth = 2 channels x 16 bits/sample (e.g. 65536:1 dynamic range) x 44.1kHz = 1_411_200 bits/second = 1.4Mbit/s Note several sources of common confusion in this unit: * 8 bits (b) = 1 bytes (B); both are commonly used for computers * k | M | G decmimal = 10^3 | 10^6 | 10^9 = 1,000 | 1,000,000 | 1,000,000,000 as used by scientists and network bandwidth engineers, k | M | G binary = 2^10 | 2^20 | 2^30 = 1,024 | 1,048,576 | 1,073,741,824 used for computer memory (megabytes) international standards say these are ki | Mi | Gi but not in common use. phone line = DS0 = 64 kbit/s modem: 28 kbit/s around here dial-up T1 = DS1 = 24 phone lines = 1.54 Mbit/s (decimal M) college to internet T3 = DS3 = 44.74 Mbit/sec ('45 Meg') 802.11b = 11 Mbit/s campus wireless ethernet = 10base-X = 10 Mbit/s ("fast ethernet") campus network or 100base-X = 100 Mbit/s or 1000base-X = 1 Gbit/s ("gigabit ethernet") USB 1.0 = 1.536 Mbit/s Firewire = 400 Mbit/s USB 2.0 = 480 Mbit/s Quick quiz: * what's the highest frequency if sampling rate is 44kHz? * how many phone lines to transfer CD quality sound at same rate it gets played? audio compact disk * http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm * http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio2/95x7.htm * http://en.wikipedia.org/wiki/Audio_CD from whatis.techtarget.com: The CD-ROM, like other CD adaptations, has data encoded in a spiral track beginning at the center and ending at the outermost edge of the disc. The spiral track holds approximately 650 MB of data. That's about 5.5 billion bits. The distance between two rows of pits, measured from the center of one track to the center of the next track is referred to as track pitch. The track pitch can range from 1.5 to 1.7 microns, but in most cases is 1.6 microns. audio CD has about 74 minutes or about 650 megabytes compression : * http://en.wikipedia.org/wiki/Audio_compression audio codecs and file formats * http://en.wikipedia.org/wiki/Codec "codec" is description of what the bit stream means "file format" is how it gets put on a disk (including headers and metadata) "lossless" .wav (http://en.wikipedia.org/wiki/WAV) FLAC (http://en.wikipedia.org/wiki/FLAC) compression designed for audio; 30-70% compression compared to 20-40% for zip "lossy" .mp3 (MPEG-1/2 Audio Layer 3) * http://en.wikipedia.org/wiki/Mp3 .ogg Ogg Vorbis * http://en.wikipedia.org/wiki/Vorbis mp3 : excellent at 256..384 kbit/s very good at 224..256 kbit/s good at 128..192 kbit/s wikipedia : Many listeners accept the MP3 bitrate of 128 kilobits per second (kbit/s) as near enough to CD quality for them; this provides a compression ratio of approximately 11:1, although listening tests show that with a bit of practice, many listeners can reliably distinguish 128 kbit/s MP3s from CD originals. To some listeners, 128 kbit/s is unacceptably low quality. Even though differences may be perceptible, this is acceptable for some listeners in some listening environments, such as a noisy car or train. encoders : LAME is an open source MP3 compression application