ISDN Codecs provide a bi-directional audio link, just like an ordinary telephone. This means that you have a high-quality link from talent to studio, but also one from the studio back to the talent. ISDN itself is bi-directional; there is no need to use additional lines and the talkback does not use bandwidth of the link in the other direction.

Modern codecs like the CDQ Prima range or AudioTX Communicator (Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to or ) allow the use of different types of audio coding for both directions. E.g. use MPEG Layer 3 from the talent to the studio, but use G722 from studio to talent. G722 has a lower audio quality, but also a lower encoding delay. Reporters in the field use that to have a high quality feed on-air, but have a low quality (but low delay) que feed from the studio.,

For a voice over application a shorter coding delay in the return feed is of course less important – it does not really make a difference if you hear the “Great! We don’t need a second take!” 100 milli seconds later then you would have over telephone…