Main parameters of digital audio

Loudness

Loudness is the human ear’s subjective perception of the intensity of a sound. Loudness is not only proportional to the log value of the loudness of the sound, but also related to the frequency and waveform of the sound. The unit of loudness is sone. Internationally, the frequency is 1kHz, the sound pressure level is 40 decibels (dB) when the loudness is 1 sone.

Tone

Tone, also known as pitch, refers to the subjective perception of the frequency of sound stimuli by the human ear. Pitch is mainly determined by the fundamental frequency, the higher the fundamental frequency, the higher the pitch, and it is also related to the intensity of the sound. Fundamental frequency refers to the lowest vibrational frequency of the articulator. The unit of tone is Mel. A tone produced by a pure tone with a frequency of 1kHz and a sound pressure level of 40dB is then defined as 1 Mel.

Timbre

Timbre refers to the subjective feeling of the human ear to different characteristics of sound, which is mainly determined by the frequency spectrum structure of the sound, but also related to the loudness, duration, establishment process and decay process of the sound.

Sampling frequency

Sampling frequency is the number of acoustic wave amplitude samples taken per second when converting an analog sound waveform to digital. The unit of sampling frequency is Hz. The higher the sampling frequency, the better the sound quality and the larger the amount of data. In multimedia, the three most commonly used sampling frequencies for CD-quality audio are 44.1kHz, 22.05kHz, and 11.025kHz.

Number of quantization bits

The number of quantization bits is to digitize the amplitude axis of the analog signal, indicating how many binary bits are used to represent the data range for each sampling point. With more quantization bits, the sound quality is better and the data volume is larger. The number of quantization bits determines the dynamic range of the data, and the number of quantization bits is 8 bits and 16 bits. There are 256 levels from minimum to maximum for 8 bits and 65,536 size levels for 16 bits.

Number of vocal channels

The number of channels refers to the number of generated sound waveforms recorded in one sampling. It is one of the important indicators to measure the sound equipment. Stereo is more expressive than mono, but with twice the amount of data.

• Mono: When recording sound, acoustic data is generated one at a time.
• Dual channel: When recording sound, two acoustic data are generated at a time.
• Stereo: Sounds are assigned to two separate channels during the recording process.
• Quasi-stereo: Audio is recorded in mono and played sometimes in stereo and sometimes in mono.
• Four-channel surround: Four pronunciation points are specified: front left, front right, back left, back right. The audience is surrounded in the middle, and can obtain the auditory feeling of being in a variety of environments.

Size calculation for digital audio

The amount of data is equal to the sampling frequency times the number of quantized bits times the number of channels /8 in bytes per second.

Bit rate

The bit rate is the number of bits transmitted per second. The bit rate is measured in bits per second (bps).The higher the bit rate, the faster the data can be transmitted. The bit rate in sound refers to the amount of binary data per unit time after the analog sound signal is converted into a digital sound signal, which is an indirect measure of audio quality.

Compression ratio

Compression ratio generally refers to the ratio of file size before compression and after compression, which indicates the compression efficiency of digital sound. In the field of audio compression, there are two compression methods: lossy compression and lossless compression. Common MP3, WMA, OGG are lossy compression, lossy compression reduces the audio sample rate and bit rate, the output audio file is smaller than the original file. Lossless compression is under the condition of saving 100% of the source file data, the audio file capacity space compression is smaller, decompressed to ensure the same size and bit rate as the source file.

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