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The selection of the sample rate was based primarily on the need to reproduce the audible frequency range of 20–20,000 Hz (20 kHz). The Nyquist–Shannon sampling theorem states that a sampling rate of more than twice the maximum frequency of the signal to be recorded is needed, resulting in a required rate of greater than 40 kHz.
The audio bit rate for a Red Book audio CD is 1,411,200 bits per second (1,411 kbit/s) or 176,400 bytes per second; 2 channels × 44,100 samples per second per channel × 16 bits per sample. Audio data coming in from a CD is contained in sectors, each sector being 2,352 bytes, and with 75 sectors containing 1 second of audio.
Sampling rate used by the Mitsubishi X-80 digital audio recorder. 64,000 Hz Uncommonly used, but supported by some hardware [18] [19] and software. [20] [21] 88,200 Hz Sampling rate used by some professional recording equipment when the destination is CD (multiples of 44,100 Hz).
Both modulations require neighboring samples to reconstruct the original waveform; the more neighboring samples, the lower the frequency that can be encoded. DSD is 1-bit, has a sampling rate of 2.8224 MHz, and makes use of noise shaping quantization techniques in order to push 1-bit quantization noise up to inaudible ultrasonic frequencies.
Audio Interchange File Format (AIFF) is an audio file format standard used for storing sound data for personal computers and other electronic audio devices. The format was developed by Apple Inc. in 1988 based on Electronic Arts' Interchange File Format (IFF, widely used on Amiga systems) and is most commonly used on Apple Macintosh computer systems.
The data compression software for encoding into ALAC files, Apple Lossless Encoder, was introduced into the Mac OS X Core Audio framework on April 28, 2004, together with the QuickTime 6.5.1 update, thus making it available in iTunes since version 4.5 and above, and its replacement, the Music application. [8]
Method 2 will work in more general cases, e.g. where the ratio of sample rates is not rational, or two real-time streams must be accommodated, or the sample rates are time-varying. See decimation and upsampling for further information on sample-rate conversion filter design/implementation.
High-resolution audio (high-definition audio or HD audio) is a term for audio files with greater than 44.1 kHz sample rate or higher than 16-bit audio bit depth. It commonly refers to 96 or 192 kHz sample rates. However, 44.1 kHz/24-bit, 48 kHz/24-bit and 88.2 kHz/24-bit recordings also exist that are labeled HD audio.