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CDQPrima USERS GUIDE

6-26-2

6.1.1.1 Stereo and Dual Mono

Users have expressed a great deal of confusion concerning the

differences between stereo, dual mono and joint stereo. From a coding

and compression standpoint, stereo and dual mono are identical. That

is, half of the total bits are assigned to the left channel, and half of the

total bits are assigned to the right channel. Left is always left, and right

is always right…no blending, no sound stage manipulations.

6.1.1.2 Joint Stereo

Unlike dual mono or stereo, joint stereo employs real-time bit allocation

techniques and dynamically assigns bits to the channels and frequency

bands that need them the most. Bits are allocated to the channel and

frequency bands that need them on a frame-by-frame basis. This

dynamic bit allocation results in considerably wider bandwidths and

higher signal-to-noise ratios than possible with the fixed bit allocation

of the other modes. If the bit allocation circuitry determines that

enough capacity is available for true stereo, then stereo frames will be

sent.

Unlike stereo and dual mono, joint stereo may manipulate the left-right

sound stage and stereo separation at high frequencies. The infinite left-

right sound stage is blended into seven locations at high frequencies

should the bit allocation circuitry deem it necessary. However, it has

been shown that any spatial blending performed by the bit allocation is

in frequency bands where the human auditory system would normally

blend stereo signals. This is one of the basic premises behind

psychoacoustic modeling. A detailed discussion of joint stereo bit

allocation techniques can be found in the CDQPrima Technical

Reference Manual.

After rigorous testing with trained listeners, joint stereo audio has been

determined to yield higher perceived audio quality than stereo or dual

mono at low bit rates, such as those encountered with single ISDN

lines.

6.1.1.3 ISO/MPEG Layer III

Recommended applications for Layer III include:

• Connecting to Layer III-only codecs

• Mix audition

• True stereo over ISDN

• High fidelity mono audio at low bit rates

MPEG Layer III

is not available

with revision 34.

Only codecs

With Revision 6

hardware

support Layer

III

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