Section 2 INTRODUCTION
36
Why did Telos select ISO/MPEG Layer III perceptual audio coding as
the primary method in the Zephyr?
Layer III is the most sophisticated method for the coding of digital audio. When
combined with ISDN, our Layer III codec (coder/decoder) makes it possible to transmit
broadcast- quality audio with the convenience, global availability, and low cost of the
dial- up telephone network.
The final report of ITU Radiocommunication Task Group 10/2 clearly recommends
Layer III for ISDN bit rates, and the daily experience of Layer III users further supports
those findings. Of course, the best way to know how good Layer III sounds in Zephyr is
to hear it for yourself.
It’s agreed that Layer III is the perfect choice for ISDN. How
come more manufacturers are not using it and why does Telos
include Layer II?
Good questions. Implementation of Layer III requires significant computer power and
carefully engineered digital signal processing (DSP). Telos Systems has been the world’s
leader in DSP for the broadcast- to- telephone interface for over a decade. We know the
technology, we know the ups and downs of connecting to telephone networks, and we
know our customers. This put Telos in a unique position to launch a sophisticated,
multifunction ISDN transceiver that supported the use of Layer III along with other
coding options.
We have implemented Layer II to offer compatibility with the installed base of users.
Layer II is the most commonly used perceptual coding scheme and products became
available before Layer III products and many users are understandably unwilling to
“retire” their old equipment.
But Layer II is used more widely for satellite program
distribution and is an important contender for Digital Audio
Broadcast. Why is this?
Layer II is currently the accepted coding scheme for applications with bit rates of
128kbps per audio channel. There is no logic, however, in concluding that because
Layer II is preferred for satellite, it should be used for ISDN. Nor is it true that if you use
Layer II in one part of your audio chain it is the best choice for all parts of the system.
Some Layer II-only manufacturers have criticisms of Layer III. Can
you address them?
Certainly. There have been interviews in several journals with Layer II- only
manufacturers who state that Layer III is too complex and too expensive. When one
considers Zephyr, it is obvious that these are unsound arguments. Complexity and cost
are design hurdles that Telos has overcome to create products that are reasonably
priced and easy to use and incorporate the most appropriate technology. There is
nothing that prevents the Layer II- only manufacturers from making the same
investment in resources and commitment to their customers. They, for whatever
reasons, choose not to do so.
Summary of Contents for Zephyr
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Page 39: ...39 SECTION 3 ZEPHYR AT A GLANCE ...
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Page 53: ...Section 4 INSTALLATION BASIC OP 53 SECTION 4 INSTALLATION BASIC OPERATION ...
Page 84: ...Section 4 INSTALLATION BASIC OPERATION 84 ...
Page 85: ...Section 5 ISDN 85 SECTION 5 ISDN ...
Page 105: ...Section 6 NON ISDN NETWORKS 105 SECTION 7 AUDIO CODING ...
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Page 119: ...Section 8 DETAILED MENU REFERENCE 119 SECTION 8 DETAILED MENU REFERENCE ...
Page 157: ...Section 9 REMOTE CONTROL 157 SECTION 9 REMOTE CONTROL ...
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Page 177: ...Section 10 ADVANCED PROBLEM SOLVING 177 SECTION 10 ADVANCED PROBLEM SOLVING ...
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Page 197: ...Section 11 TECHNICAL INFORMATION 197 SECTION 11 DETAILED TECHNICAL INFORMATION ...
Page 219: ...Section 12 SCHEMATICS 219 SECTION 12 SCHEMATICS ...
Page 221: ...Section 13 MANUFACTURER S DATA SHEETS 221 SECTION 13 MANUFACTURER S DATA SHEETS ...
Page 223: ...Section 14 SPECIFICATIONS WARRANTY 223 SECTION 14 SPECIFICATIONS AND WARRANTY ...
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Page 229: ...Section 15 APPENDICES 229 SECTION 15 APPENDICES ...