Audio CD files use the uncompressed Pulse Code Modulation (PCM) format, defined by the Red Book standard.
Audio CDs, the standard compact discs designed specifically for playing audio, utilize a specific and well-defined format to ensure compatibility across different players. This format is officially known as the Red Book standard, part of the Rainbow Books collection of CD specifications.
Understanding the Red Book Standard
The core of the Red Book standard for audio CDs specifies the digital format used for storing sound. It dictates several key parameters for the audio data:
- Encoding: Uncompressed Pulse Code Modulation (PCM)
- Sample Rate: 44.1 kilohertz (kHz)
- Bit Depth: 16-bit resolution
This combination results in high-fidelity audio playback, capturing sound with sufficient detail for music listening.
What is Uncompressed PCM?
PCM is a method used to digitally represent analog signals. In this context, the original analog audio waveform is sampled thousands of times per second (the sample rate), and the amplitude of each sample is recorded as a digital value (determined by the bit depth). "Uncompressed" means that the digital data is stored exactly as it is captured, without using any data compression techniques to reduce file size. This ensures maximum audio quality but results in larger file sizes compared to compressed formats like MP3.
Red Book Specifications
Here's a quick look at the standard specifications:
| Feature | Specification | Detail |
|---|---|---|
| Format | Uncompressed PCM | Pulse Code Modulation |
| Standard | Red Book | Standard for audio CDs |
| Sample Rate | 44.1 kHz | Samples taken 44,100 times per second |
| Bit Depth | 16-bit Resolution | 65,536 possible amplitude values |
| Channels | Stereo (2 Channels) | Typically two channels (left/right) |
The Connection to WAV Format
The reference material notes that the format used on audio CDs is commonly referred to as waveform audio file (WAV) format. While technically, a file copied from a CD often ends up in a .wav file container on a computer, the native format on the CD itself conforms to the Red Book's PCM specification, which is the underlying data format also used within a WAV file.
Essentially, a standard WAV file is a digital container that holds raw, uncompressed PCM audio data matching these exact specifications (44.1 kHz, 16-bit, stereo). Therefore, ripping an audio CD typically extracts this PCM data and places it directly into a WAV file.
In summary, the audio data on a CD is in an uncompressed PCM format adhering to the Red Book standard, which is fundamentally the same data format commonly stored in a WAV file.
