I have recently experienced a background noise from the output audio of the Telos Zephyr 9200. The noise is not a typical ground loop hum but a strange tickling noise like it is from a clock burst signal from somewhere lacing into my analog audio feed going into and out of the zephyr 9200.

The system is used for a bi-directional feed to and from a remote radio studio using a 56K point-to-point private line (DDS) running from California (my end studio) to Texas (remote studio). The Zephyr 9200's V.35 port is connected to an Adtran DSU 56/64 which interfaces with the point-to-point circuit. We use G.722 encoding/decoding scheme.

I have used this circuit for many years but never had this kind of problem. The said noise seems to amplify into a very noticeable level on the remote end. By the time the decoded audio (analog) from the remote-end is fed to the radio transmitter, the noise becomes a constant 'u' sound, quite a nuisance on the air. I have checked with the phone company that provide the 56K circuit. However, they were dumbfounded on what to do except to tell me that the circuit test came back digitally clean (no bit error). Not much that they can go on except advising me to recheck my end equipment.

I do have the sample noise captured onto an .mp3 file (I just don't know how to attach it to this message).

I appreciate any of your input on how to to pinpoint the source of the problem. By the way, if Mr. Rolf Taylor of Telos-Systems (I met him a couple of years back at NAB) is on line, it would be great to hear from him.

Thank you.

Hello Edwin,

Thank you for the "loop back" suggestion. I will try to do it and hopefully be able to isolate the problem. It seems to be more of an interference issue, be it from the Zephyr unknowingly encoding the noise or the phone line issue.

I forgot to mention that the remote end in Houston was relocated lately. That local loop end was recently moved to a new address.  The problem seems to start at that time. However, the phone company is unwavering in my quest to fix the problem except blaming it on my equipment end that inherits the interference from the new surrounding or my audio feed is not clean. Hopefully the loop back test would give me a better idea.

About the G.722 algorithm, I am stuck because all of our existing setup are fixed on this scheme (for its low-delay characteristics), and my technical support resource on the other end is very limited and outsourcing based.

Our setup includes a private line (leased line) which is essentially a full time ISDN line where we don't have to dial up for connection just like modem dial-up vs. DSL for Internet. We use it because it costs much less particularly for our 24 hr remote feed needs. It is also bi-directional, a good thing for talk-show between studios on both ends.

I did leave a message for Mr. Taylor this morning. I am waiting for his return call.

Thank you so much for your input and for having this forum. It is very helpful indeed.

Sincerely,

Joe Dinh