Traditional lossless compression methods (Huffman, LZW, etc.) are usually poorly applied to compressing audio information (for the same reasons as when compressing visual information).
Some lossy compression methods are listed below:
Compression of silence (pauses) – defines periods of “silence”, works similarly to run-length coding.
ADPCM – Adaptive Differential Pulse Code Modulation (the term Adaptive Delta Pulse Code Modulation (ADPCM) is used in Russian literature. For example, the CCITT G.721 standard is from 16 to 32 Kbits / sec:
Encoding the difference between two or more consecutive samples; then the difference is quantized -> when quantizing, part of the information is lost. The quantization is adaptive (changes the parameters depending Continue reading
For the normal average organ of hearing of a person, there are some limit (threshold) minimum values of the physical parameters of the sound field, at which there is still an auditory sensation. Such a threshold of audibility is the standardized sound intensity I0 = 10 … 12 W / m2 (close to the threshold of audibility at f = 1000 Hz in silence), as well as the corresponding sound pressure p0 = 2 * 10-5 Pa and sound energy density e03 * 10-15 J / m3. The hearing threshold is private dependent. Above the threshold of hearing is the hearing area. In fig. 1 shows a curve of the threshold of audibility. The upper threshold of audibility is also shown there, above which the destruction of the organ of hearing can occur – the pain threshold, which corresponds to pressure pmax = 150 … 200 Pa, which exceeds 107 times p0 = 2 * 10-5 Pa. Continue reading
Classically, the sound spectrum is divided into three parts: low, medium and high frequencies. The frequency limits, although not everyone agrees with this, can be defined as follows: low from 10 Hz to 200 Hz, medium from 200 Hz to 5 kHz, and from 5 kHz – high. For a more precise definition, let’s divide these three parts into smaller ones and consider them separately.
1) Low bass (from 10 Hz to 80 Hz) – these are the lowest notes from which the room resonates, and the wires begin to hum. If your sound reproducing equipment does not reproduce these frequencies, you should feel the loss of saturation and depth of sound. Naturally, when recording and mixing, the loss of these frequencies will cause the same effect.
2) Upper basses (from 80 Hz to 200 Hz) are the top notes of bass instruments and the lowest notes of Continue reading