Computer Science E-1: Understanding Computers and the
Internet
Harvard Extension School
Fall 2006
In this workshop, we will look at the origins of digital
audio and how sound is manipulated using computers.
Common audio formats and technical qualities will be reviewed.
By the end of the workshop, students should be able to rip a track off a CD,
record a sound, edit the two tracks together, create a fade, and burn a CD.
A discussion of the types of software available and how they are used in digital
audio will end the session.
* 8,000 Hz - telephone, adequate for human speech
* 11,025 Hz
* 22,050 Hz - radio
* 32,000 Hz - miniDV digital video camcorder, DAT (LP mode)
* 44,100 Hz - audio CD, also most commonly used with MPEG-1 audio (VCD,
SVCD, MP3)
* 47,250 Hz - world's first commercial PCM sound recorder by Nippon Columbia
(Denon)
* 48,000 Hz - digital sound used for miniDV, digital TV, DVD, DAT, films
and professional audio
* 50,000 Hz - first commercial digital audio recorders from the late 70's
from 3M and Soundstream
* 50,400 Hz - sampling rate used by the Mitsubishi X-80 digital audio recorder
* 96,000 or 192,000 Hz - DVD-Audio, some LPCM DVD tracks, BD-ROM (Blu-ray
Disc) audio tracks, and HD-DVD (High-Definition DVD) audio tracks
* 2.8224 MHz - SACD, 1-bit sigma-delta modulation process known as Direct
Stream Digital, co-developed by Sony and Philips
Audio (MP3)
* 32 kbit/s - MW (AM) quality
* 96 kbit/s - FM quality
* 128 - 192 kbit/s - Typical "acceptable" quality
* 224 - 320 kbit/s - Medium-high quality to near audio CD quality
Other audio
* 4 kbit/s - minimum necessary for recognizable speech (using special-purpose
speech codecs)
* 8 kbit/s - telephone quality (using speech codecs)
* 500 kbit/s - 1 Mbit/s - lossless audio as used in formats such as FLAC,
WavPack or Monkey's Audio