History of Sound – Analog vs Digital

When CDs were first introduced in the early 1980s, their single purpose in life was to hold music in a digital format. In order to understand how a CD works, you need to first understand how digital recording and playback works and the difference between analog 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. This is an analog recording of sounds and over time it evolved so that recordings were made electronically rather then scratched on tin foil and drastically improved the fidelity of the recording. These recordings are in the form of an analog wave.

Digital Data (CD or other digital recording)

The goal for digital recordings 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. This is accomplished by converting the analog wave to a digital recording (a series of numbers). This is done via an analog-to-digital converter (ADC). To play the music, these numbers are converted back to an analog wave using a digital-to-analog (DAC). The analog wave that it produces is amplified and sent to the speakers to produce the sound.

Digital Quality

When you take an analog wave and convert it with an analog-to-digital converter, you have control over two variables: the sampling rate (how many samples are taken 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 analog waveform close enough that the sound is essentially 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 can be divided in three basic 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), which is usually stored as a .wav on Windows or as .aiff on Mac. WAV and AIFF are a flexible file formats that can store any combination of sampling rates or bit rates. This is the file format used on Cds.
  • Lossless Compression: Lossless compressed formats require more processing for the same time recorded, but are more efficient in terms of 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 audio 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 the MPEG-1 Audio Layer 3 (MP3). MP3 uses a form of lossy data compression.