History of Sound
Analog vs Digital
First introduced in the early 1980s, the single purpose in life for a CD was to hold music in a digital format. To understand how a CD works, you need first to understand how digital recording and playback works and the difference between analogue and digital technologies.
The First Recording & Playing of Sound
In 1877 Thomas Edison created the phonograph, using tin and vibrations to record and playback sounds. In 1887, Emil Berliner created the gramophone which used flat records with spinal groove over instead of tin and made reproducing records easy. It is an analogue recording of sounds, and over time it evolved so that recordings were made electronically rather than scratched on tin foil and drastically improved the fidelity of the recording. These recordings are in the form of an analogue wave.
Digital Data (CD or other digital recordings)
The goal for digital is to create a very high fidelity (very high similarity between the original signal and the reproduced signal) and perfect reproduction. Over time, an LP will wear, and the playback becomes degraded over time. With a CD it will play the same the hundredth time as it did the first. Accomplished by converting the analogue wave to a digital recording (a series of numbers). Done via an analog-to-digital converter (ADC). To playback the music, these numbers are converted back to an analogue wave using a digital-to-analog (DAC). The analogue wave that it produces is amplified and sent to the speakers to produce the sound.
When an analogue wave is converted it with an analog-to-digital converter, you have control over two variables. The sampling rate (how many samples per second); and, the sampling resolution more commonly referred to as the bit rate (accuracy of each measurement taken of a waveform). Typically, the sampling rate for a CD is 44,100 samples per second (44.1 kHz) with a bit rate of 65,536 (16 bit or 64kbps/channel). This output level matches the original analogue waveform close enough that the sound is virtually perfect to the human ear.
File Formats and Codecs
An audio file format is essentially a container for storing audio information in digital format. The many formats of audio file formats and codecs are in three primary groups: uncompressed audio file formats, lossless compression audio formats and lossy compression audio file formats.
- Uncompressed: The most used and known uncompressed audio file format is Pulse Code Modulation (PCM), usually stored as a .wav on Windows or as .aiff on Mac. WAV and AIFF are flexible file formats that can store any combination of sampling rates or bit rates. It is the file format used on Cds.
- Lossless Compression: Lossless compressed formats require more processing at the same time recorded, but are more efficient regarding disk space used. The most common lossless compressed format is Free Lossless Audio Codec (FLAC). FLAC file is an audio format similar to MP3, but lossless, meaning that the audio information is compressed in FLAC file without any loss in its sound quality. Similar to how Zip works, but you will get much better compression rate because FLAC it is designed specifically for audio files.
- Lossless Compression: Lossy compression audio file formats are the most used audio formats on the Internet, computers and other multimedia equipment. The most popular is MPEG-1 Audio Layer 3 (MP3). MP3 uses a form of lossy data compression.