Telos ZephyrExpress user manual Layer 3 Joint Stereo

Layer 3 Joint Stereo

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A joint stereo mode permits advantage to be taken from the redundancy in stereo program material. The encoder switches from discrete L/R to a matrixed L+R/L-R mode dynamically, depending upon the program content. The matrixed mode of operation takes of advantage of the usual redundancy of the “center” channel information and therefore significantly improves overall fidelity.

WARNING!

Joint stereo takes advantage of the way sounds distribute themselves over a normal stereo field. If youÕre transmitting two signals that donÕt comprise a normal stereo field Ñ as would be the case if youÕre transmitting an MS matrixed signal or two totally independent audio channels ÑÊit wonÕt save you anything.

CURIOSITY NOTE!

Layer 3 is the direct successor to the ÒASPECÓ algorithm, which was based on coding methods by Fraunhofer/University of Erlangen, AT&T, Thomson Consumer Electronics, and CNET (Centre National dÕEdudes des TŽlŽcommunications).

In the first tests for ISO in 1990, ASPEC showed the best sound quality, with an advantage at lower bit rates. The precursor to the Layer 2 algorithm Ñ originally called MUSICAM1 Ñ had the advantage of lower complexity and simpler processing. L3 came from a merging of both systems: For easier transcoding, L3 adopted the L2 filterbank for the first stage, and the bitstream rate was adjusted.

ISO/MPEG LAYER 2

MPEG Layer 2 is the world’s most popular perceptual coding method, primarily because it’s easier and less expensive to implement — particularly at the encoder — and practical devices using it were available earlier than Layer 3. It’s a preferred choice for applications where very large data capacity is available, such as satellite links, high-capacity Primary ISDN or T1 circuits, and hard disk storage systems using Ethernet for signal distribution.

We include it in ZephyrExpress to offer compatibility with the widest variety of codecs.

Our implementation is the highest quality, using DSP code licensed directly from the algorithm’s primary inventor: the IRT in Munich.

1While “Musicam” was the original European developer’s name for a particular coding process, it was subsequently registered as a product trademark by a US company...

forcing world-wide users to drop the name and use “Layer 2” instead. That company’s products and the internationally-accepted algorithm have nothing to do with each other, except that ISO/MPEG Layer 2 is one of the processes supported by the products.

CODING 5-7