Digital audio

Digital audio refers to the use of digital encoding, that is, the use of zeros and ones to record audio information, as opposed to analog audio. Before the advent of CD and computer technology, there was analog audio (such as audio tape), in which the digital/analog converter is referred to as DAC and the analog/digital converter is referred to as ADC.

Digital audio several important parameters

Sampling digit

Can understand the resolution of digital audio equipment processing sound, that is, the degree of discrimination of sound. Just like the number of digits representing colors (8 bits for 256 colors, 16 bits for 65536 colors), there are 8 bits, 16 bits, 24 bits, etc. The higher the number, the higher the resolution and the truer the sound recorded and played back.

Sampling frequency

It is how many times a second the sound is sampled to record the digital information. For example, CD audio has a sampling rate of 44.1KHz, which records information on sound at a frequency of 44,100 times per second. In principle, the higher the sampling rate, the better the sound quality.

In the field of digital audio, the sampling rates commonly used are:

  • 8,000 Hz – A telephone sampling rate that is sufficient for human speech
  • 11025 Hz
  • 22,050 Hz – Sampling rate used for radio broadcasting
  • 32,000 HZ-MinidV Digital video camcorder, DAT (LP mode) sampling rate
  • 44,100 Hz – audio CD, also commonly used for mpeg-1 audio (VCD, SVCD, MP3) with the sampling rate
  • 47,250 Hz – The sampling rate used for the world’s first commercial PCM recorder developed by Nippon Columbia (Denon)
  • 48,000 HZ-The sampling rate used for digital sound for miniDV, DIGITAL TV, DVD, DAT, film and professional audio
  • 50,000 Hz – The sampling rate used by the first commercial digital recorder developed by 3M and Soundstream in the late 1970s
  • 50,400 Hz – sampling rate used for mitsubishi x-80 digital recorder
  • The sampling rate used for 96,000 or 192,000 HZ-DVD-Audio, some LPCM DVD tracks, BD-ROM (blue disc) tracks, and HD-DVD (high definition DVD) tracks
  • 2.8224 MHz – sampling rate used in 1-bit Sigma-Delta Modulation process called Direct Stream Digital developed by SACD, SONY and Philips.

Bit rate

BPS (bit per second) indicates the number of bits transmitted per second. As a reference index for the compression efficiency of digital music, KBPS (colloquially 1024 bits per second) is usually used as a unit.

The compression ratio

Usually refers to the ratio of the size of a music file before and after compression, used to simply describe the compression efficiency of digital sound.

Size of the audio

The size of a digital audio file is calculated as follows: Data quantity Byte= Sampling frequency Hz x (sampling bits /8) x Number of channels x Time (s)

For example, if the sampling frequency is 44.1khz, the resolution is 16 bits, the stereo, and the recording time is 10s, what is the size of the sound file conforming to the CD-quality sound?

According to the calculation formula: data quantity Byte=44100Hz x (16/8) x 2 x 10s=1764KByte and then converted to the corresponding unit

Suppose the audio size is len, then the data size of one channel is: Len/number of channels/(sampling bits /8)