Available online
Description
The programme demonstrates some of the problems involved in the design of telephone terminals incorporating loudspeakers.
The programme demonstrates some of the problems involved in the design of telephone terminals incorporating loudspeakers.
| Module code and title: | T321, Telecommunication systems |
|---|---|
| Item code: | T321; 15 |
| First transmission date: | 18-09-1976 |
| Published: | 1976 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:22:23 |
| + Show more... | |
| Producer: | David Saunders |
| Contributors: | Martin Hartley Jones; Chris Pinches |
| Publisher: | BBC Open University |
| Keyword(s): | Acoustic characteristics; Audio feedback; Conference situations; Frequency shifting; Hands-free; Sweep frequency generator |
| Footage description: | Chris Pinches introduces the programme with a brief discussion of some uses of loudspeaker systems for telephones. Pinches, using an animated diagram and electronic apparatus, demonstrates the difficulties encountered when amplifying sound levels of an ordinary telephone. The demonstration results in a loud howl. Pinches explains the cause of this instability. Martin Jones in a room built to provide relevant acoustic feedback. He points out the characteristics of the room and goes on to explain that audio feedback (howl) depends on these characteristics. Chris Pinches performs an experiment to measure the frequency response of the above room. The result is traced by pen recorder. Pinches examines a small, magnified portion of this trace. He points out the reason for the instability in the system which results in howl. Pinches, again using the magnified trace, explains the effects of flattening the peaks in the signal and raising the average level. He goes on to explain one technique, equalisation, for achieving this. Pinches then discusses, using the above trace again, the technique of frequency shifting which has the same effect of averaging acoustic responses of a room. Martin Jones gives a practical demonstration of the use of frequency shifting to overcome howl in loudspeaker telephone systems. He explains the apparatus and then does two demonstrations - one to eliminate howl, the other to eliminate coloration as gain is increased. Jones summarises the technique of frequency shifting. Chris Pinches sums up the programme. |
| Master spool number: | 6HT/71954 |
| Production number: | 00525_5234 |
| Videofinder number: | 1356 |
| Available to public: | no |
