Dual Channel/stereo/joint stereo concept Differentiation

From: http://blog.csdn.net/worldpharos/archive/2009/12/22/5056354.aspx

Dual Channel: it consists of two single channels. When two channels are encoded, the correlation is not considered. The bit rate of each channel is half of the total bit rate of the audio. E. g In a 128 kbits file each channesl woudle take 64 kbits.

Stereo: it consists of two or more independent channels. The bit rate of each channel depends on the amount of information its respective codes contain. When you hear this, you can locate the audio source. E.G right use 48 kbits and left uses 96 kbits in a 128 kbits file. Data correlation between two channels is not calculated, but data traffic of the two channels is allocated in a coordinated manner, and more bits are automatically allocated to the complex channels.

Joint STEREO: it is also composed of two channels, but the encoding takes into account the common information of the two channels, which is more compressed than stereo. In this compression mode, lame calculates data correlation between two channels. When the left-right channel data is similar, the M/S (MID/side) encoding technology will be used to calculate the central channel (L + r) and the two sides of the channel difference (L-R) value, A large number of BITs are allocated to the central channel to increase the data record bandwidth.

Single and Double channels refer to one or two audio processing system circuits. Stereo refers to the audio source. The most basic stereo sound requires two sound devices to enable the sound to become stereoscopic after being heard by the ears.

To enable stereo sound, the player must have at least dual channels. The left and right audio channels of the audio source are fed into the dual-channel amplification circuit and are finally played out through the speaker.

Audio digitalization digitizes the continuous analog audio waveforms, including the sampling frequency, sampling digits, and sampling accuracy. The two determine the quality of digital audio. Another important factor reflecting the digital quality of audio is the number of audio channels. When recording a sound, if a sound wave data is generated each time, it is called a single channel. Every time two sound waves are generated, it is called a stereo sound (that is, a dual channel), the stereo sound can reflect the human hearing more realistically.

Stereo Sound is not equal to dual-channel. The general introduction should be that the stereo sound must be composed of dual-channel, but the dual-channel is not necessarily stereo because the stereo sound is recorded based on the dual-ear effect principle, if a single-channel audio source is divided into two channels, it cannot be called a stereo sound. A stereo sound is characterized by the ability to locate the sound left and right.

In the sound system, two or more sound channels are used to enable the relative spatial location of the sound source felt by the listener to be close to the relative spatial location of the actual sound source. This replay sound is called a stereo sound. Stereo Sound has dual-channel stereo, four sound channel stereo, Dolby stereo, Dolby surround sound, Dolby AC-3 Digital surround sound and so on.

Joint stereo is a stereo encoding technique, mainly divided into intensity stereo (is) and MID/side (m/s) stereo. Is is used in relatively low-traffic scenarios. It uses the human ears's insufficient ability to determine the direction of low-frequency signals and splits the low-frequency audio data into single-channel data, the remaining high-frequency data is combined with another single-channel data, and the location information of the high-frequency data is recorded to reconstruct the effect of the stereo. For example, a piano solo recording can be used to reduce the amount of music field information in a limited amount of data traffic, but greatly increase the tone information.

Mid/side (m/s) stereo is often used when the left and right channels have a large data similarity. The recording method is to merge the left and right channels (L + r) to obtain a new track, then the Left and Right audio subtraction (L-R) to get another track, and then the two track data with the above mentioned auditory psychology model and filter processing. Like mid/side (m/s), stereo and is use the loss of some phase (phase) Information to generate a higher tone record information. Generally, MP3 is used in combination with Mid/side stereo and intensity stereo, depending on the data content and traffic. For MP3 with a higher traffic rate of kbps or higher, the two audio channels in the stereo sound can be separately encoded to save the phase information.

If you often create MP3 by yourself, you may have encountered terms such as mono, joint stereo, and stereo. They are different audio channels. "Single Channel" and "stereo" are familiar to everyone. So what is this "combined stereo? What is the difference between it and "stereo?

After verification and consideration, I come to the following conclusions for your reference only.

The "combined stereo mode" is one of the Audio Encoding stereo modes. The combined stereo mode makes full use of the similarities between the left and right audio channels. The same part of the left and right audio channels are not repeatedly encoded, reducing data waste, in this way, more details can be displayed at a lower bit rate. For audios with little difference between left and right channels, the combined stereo encoding mode usually achieves good results at a low bit rate.

The "stereo mode" uses two independent channels for encoding. Therefore, it requires a large bit rate, but its left and right channels have a high degree of separation, generally, high bit rate is used for high-quality audio encoding.

Based on experience, it is more appropriate to use the 128 kbit/s bit rate and the combined stereo mode when making general mp3 songs. An English document is provided here:

Q: What's the difference between the various stereo modes?

A: It's important to understand the difference between stereo and joint stereo. 'Joint stereo 'modes take advantage of the similarities between the L + R channels. this allows more bits to be used in other areas and in our cases this can give an overall gain in encoding quality. almost all encoders use joint stereo when encoding at 128 kbits.

Joint stereo has 2 submodes called is and Ms. 'Joint stereo is 'destroys phase information and shouldn' t be used for high-quality encoding. 'Joint stereo Ms' means middle/side and is OK for use in most encoding.

However, for some audio, joint stereo MS may create a 'flanging' or

'Swishing' effect. in these cases it's better to use 'stereo mode '. this mode creates 2 independent channels for both left and right. when stereo mode is used, you shoshould also use a higher bitrate (160 or 192 kbits)-stereo mode will allocate about half of this bitrate for each channel.

In summary, for most audio, joint stereo MS at 128 or 160 kbits shoshould be fine. if your audio is especially 'wide 'and creates flange you shoshould use 'stereo' mode. you can change these modes in the radium codec control panel.