iTunes

iTunes Support

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Use iTunes to encode one of the songs you have ripped from a commercial CD (the shorter, the better!) into the following formats:

Format
File_Name

.WAV
44.1 kHz
16 bit (64kbps/channel)
stereo

standard.wav
.WAV
44.100 kHz
16 bit
mono
standard_mono.wav
.WAV
11.025 kHz
16 bit
stereo
low_sample_rate.wav

.WAV
44.100 kHz
8 bit
stereo

low_bit_rate.wav

.AIFF
44.100 kHz
16 bit
stereo

standard.aiff

.AIFF
make the file size small,
yet sound acceptable

acceptable.aiff

AAC
44.100 kHz
128 kbps
stereo

standard.m4a
AAC
make the file size small,
yet sound acceptable
acceptable.m4a
.MP3
44.1 kHz
128 mbps
stereo
standard.mp3
.MP3
make the file size small,
yet sound acceptable
acceptable.mp3

Save your files in a folder called audio_formats on your disk. Submit the folder on a data CD.

Bit Depth

Also known as Sampling Resolution, Bit Depth, Bit Resolution, or Bit Rate. When a snapshot or sample of a sound is taken, the analog-to-digital converter produces a series of binary numbers (bits) to describe the sample. The sampling resolution describes how many bits - as in “0s” and “1s” - are available to describe a digital recording.

In practice, the bit resolution defines the dynamic range of a sound . The dynamic range of a sound represents the difference between the softest sound present in a recording and the loudest sound. An 8-bit digitizer has a dynamic range of 96dB. By comparison, the dynamic range of the human ear is approximately from silence to 120dB.

Sample rate describes how frequently (or the amount of time between sample intervals) an analog audio signal is “sampled” or analyzed by the analogue-todigital converter as it is recorded and converted to a digital format. For example, the standard sample rate for Compact Discs is 44.1 kHz. Which means 44,100 (or 44.1kHz) samples (or ‘snapshots’) are taken each second to convert the sound into a digital format.

In practice, the sample rate defines the frequency range of a digital recording. Sample rate directly affects audio fidelity in terms of upper frequency response: the higher the sample rate, the higher the available frequency response. A fundamental principle of sampling states that to accurately capture a sound, the sample rate must be at least twice the highest frequency in the sound. Higher sampling rates yield better sound fidelity and larger sound files.

Common Sample Rates

96.000kHz - This is the standard sample rate for Digital Video Disc (DVD) audio, and is often used by sound editors working in audio postproduction for DVD. This rate results in an upper frequency response of 48kHz — well above the range of human hearing.

48.000kHz - This is one of two standard sample rates for digital audio tape (DAT) recorders, and is often used by sound editors working in audio post-production for video or film. This rate results in an upper frequency response of 24kHz - well above the range of human hearing.

44.100kHz - This is the standard sample rate for Compact Discs, digital audio tape (DAT) recorders, and high-fidelity audio applications on Macintosh and PCcompatible computers with 16- bit playback capability. It is sometimes called “ forty-four one” (as in 44.1kHz). Most sound engineers working in music production – or anything that may be distributed on a CD — work at this rate. This rate results in an upper frequency response of 22,050Hz — above most people’s hearing range.

22.050kHz & 11.025kHz - These sample rates are sometimes used for lowerfidelity audio playback on Macintosh and PC-compatible computers. Many games, web-sites and other multimedia productions utilize 22.050kHz (or lower) 8-bit audio, since it uses half the disc space of CD quality audio. The 22.050kHz sample rate results in an upper frequency response of 12.025kHz; this may sound “muffled,” since most people can hear considerably higher frequencies than 12.025kHz.

Source: Darren Fisher

Note: 1 kilobit = 1,024 bits. Go figure!

Copyright ©2003 L Garcia