Question 23/XV - Encoding of speech signals into bit rates of less than
16 kbit/s
(Continuation of Question 32/XVIII 1985-88)

Considering

(1) that progress in the studies of speech signal encoding indicate that
reasonable speech quality may be possible at bit rates significantly
less than 16 kbit/s, e.g. 8 kbit/s;

(2) that certain areas of communications may have applications for
speech signal encoding at bit rates of less than 16 kbit/s,

1. What bit rate(s) less than 16 kbit/s should be recommended for
encoded speech signals?

2. What algorithm(s) should be recommended for encoding speech signals
into this (these) bit rate(s)?

3. What test methods and conditions should be recommended to test the
relevant performance of hardware which incorporates the recommended
algorithm(s)?

4. What should be the recommended area(s) of application of the
recommended algorithm(s)?

5. What should be recommended to allow extension to other bandwidths?

Points for study

1.The application and performance requirements that should be
considered.

2.The test methods and conditions that should be used to select any
encoding algorithm(s) to be recommended.

3.The assessment measures that should be used to evaluate the quality of
speech processed using the recommended algorithm(s);

4.Speech analysis/synthesis techniques.

5.Network considerations and constraints, e.g. delay and interaction
with echo control.

6. Extension to provide wide bandwidth speech.

Notes

1. Account should be taken of the work in Study Group XII on speech
performance aspects of digital systems and integration of mobile systems
into the public switched networks, and subjective evaluation.

2. Account should be taken of the work in Study Group XVIII on ISDN and
general network issues.

3. Account should be taken of the studies carried out under Questions 3,
4 and 10/XV.

4. INMARSAT have reported activity within the Airlines Electronic
Engineering Committee on codecs operating at 4.8 to 9.6 kbit/s for use
in telephone communications in commercial airlines.

5. Land mobile satellite use of voice codecs operating between 4.8 and
9.6 kbit/s is also subject to activities in several organizations for
commercial telephone communications.