Multi-channel digital audio encoding
system and its application
Henrique S. Malvar
Microsoft Research
One Microsoft Way
Redmond, WA 98052, USA
Abstract
With the storage media capacity and transmission bandwidth continues to improve, high-quality multi-channel digital audio systems are gradually replacing the traditional single-channel, Stereo system, while becoming a new media way. This article focuses on the current of several typical multi-channel digital audio system, encoding and decoding technology. With MPEG-2, AC-3, DTS, MPEG AAC multi-channel digital audio systems to discuss their respective channel configuration, data capacity, data rates etc. Bring the advantages and disadvantages, the final presentation in the digital audio and video broadcasting, multi-channel digital audio systems applications.
1. Introduction
For the CD format is concerned, we all know that it has a good signal to noise ratio more than 80dB dynamic range over and over 15kHz frequency range, which Makes it have good audio quality and satisfactory listening experience, but it only provides two channels. Multi-channel digital audio system, through the channel Expansion, not only in terms of quality comparable with the CD audio, but also give the audience an immersive experience, which is the traditional mono and stereo without Method to achieve, so multi-channel digital audio system has been greater audience acceptance, but also gradually became the mainstream of music production.
Among the many international standards, such as SMPTE, EBU, ITU-R, ISO / IEC, MPEG and so on, are covered with a 5.1-channel multi-channel called the number of Word audio format. In the forthcoming DVD-Audio standard, also provides for use of 24bit sampling accuracy, 88.2,96,192 KHz sampling rate of the multi-Channel digital audio formats.
A widely accepted multi-channel digital audio system configuration is what we commonly known as the 5.1-channel system, which is 3/2/.1 configuration program. This Ways in accordance with the recommendations of ITR-U for the replay BS.775 to determine the placement of the speakers.
2.multi-channel digital audio encoding
From stereo to multi-channel transition, increasing the need for storage and transmission media needs. Here in CD format, for example, assume that the sampling frequency of Fs = 44.1kHz, sampling accuracy of R for 16bit, then the CD format audio data rate of B as follows:
BCD = 2 * R * Fs = 1.411Mb / s
This shows that the one-hour music CD format, needs 635MB of storage space, in fact, the longest CD playback time for 74 minutes. Well, if so Using a multi-channel when the data rate at this time as follows:
Bcdmultichannel = 5.1 * R * Fs = 3.598Mb / s
The same one-hour multi-channel format of the music is to 1.62GB of storage space, far larger than the CD capacity. At the same time the current has been applied to multi-Channel systems are faced with bandwidth issues. Such as digital television in the United States only to the multi-channel audio 384kb / s of bandwidth in the Internet audio-Canton Broadcast in only 56kb / s data channels, so clear from the foregoing, multi-channel digital audio systems are faced with those storage capacity and transmission bandwidth limitations.
How to multi-channel digital audio data rate reduction at the same time can guarantee the audio quality is a multi-channel digital audio systems are faced with major problems. Public
Is well known, for linear PCM, it#39;s simple, in high-capacity / high bandwidth available under the premise of CD-quality audio signals. From another Perspective, the sampling accuracy improvement, as well as increased sampling frequency will result in higher audio quality, if the sampling accuracy by up to R = 16 R = 24; the sampling frequency Fs = 44.1kHz, or by Fs = 48kHz to Fs = 96kHz, or Fs = 192kHz. This development trend has gradually by a number of Recording engineers and music producers accepted by the same multi-channel digital audio system is going to follow this trend. But if they remain linear PCM, this is undoubtedly a greater increase in the amount of data to improve the existing data rate.
We know that the linear PCM audio signal does not take full advantage of the characteristics of encoded PCM data stream in the presence of a large number of redundant information. At the same time Want to emphasize is that no matter how the audio signal encoding and decoding, transmission, and ultimately depends on our human ear to be achieved, so we can fully consider the human ear#39;s auditory characteristics and take advantage of, such as the human ear#39;s masking effect, Haas effect and so on. This allows the audio letter
No. related with that part of the human ear to get rid of redundant information in the encoding is useful only to that part of the audio signal is encoded, thereby reducing the amount of data involved in coding. At the same time coded signals and then the distribution of bit precision, for larger amplitude signals or relatively fast changes in the signal to allocate more bits, and for a small increase, changing the signal slowly decreased the distribution of bits to achieve the reduction of the possibility of data rate to achieve coding efficiency. Of course, this result is based on a complex encoding process into a price. The following detailed analysis of several acoustic models.
2.1 Based on degree of auditory domain encoded signals that can be heard
The human ear to the voice of the feeling of vibration in the frequency and sound pressure level of certain aspects of the scope, frequency range of normal is about 20Hz ~ 20kHz, while the sound pressure level range is show
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