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66. You Must Remember This     by Dave Immer   8/13/15

A codec deals with the audio. ISDN deals with the connection. IP is an alternative to ISDN with a (usually) higher average bit-rate but also some data loss.

ISDN connections are phone calls that are circuit-switched data and carried over the worldwide PSTN (Public Switched Telephone Network) along with traditional POTS voice calls. Each call has a fixed bit-rate of 64kbs. ISDN connections have bit-rates in multiples of 64kbs. Connections are private.

IP connections  are streaming media that are packet-switched and carried over the worldwide internet along with Netflix, Google, Amazon, Skype, email, etc. Data packet delivery competes with and shares the path of other internet traffic. Connections can have specified bit-rates limited only by service bandwidth. Connections can accommodate multiple participants.

Check Send & Receive.
Whether your live audio network is ISDN or IP, I urge you to adopt these as standard practices.
For a studio, where routing and patching can change depending on the job requirements, it’s a good idea to do a loop-back test prior to establishing the connection. This way you can track down your send signal to the codec and receive signal from it so there is no groping once the connection is live. But for a one-person, home- setup, the routing and levels are unlikely to change from session to session.

Remember, for a good loop-back test you can either dial your 2nd line from the 1st or call 732-758-9999 from as many lines as you need.

Comments and questions welcome.