Review: IP DTL broadcast IP voice link

Remote interviews

Audio Mixer
In the mix: systems such as IP DTL work best with a mixer at the studio end. Picture: ENS Media

Since the 1980s, the mainstay of remote audio contributions, on both radio and TV, has been the ISDN line.

Run as part of the public phone network, ISDN is a digital service capable of handling data streams directly – rather than via a modem, as was the case with analogue “dial up” lines. ISDN quickly became the method of choice for live commentary, interviews, and voiceover work.

By today’s standards, ISDN’s data speeds are paltry: 64kbps per “channel”; in the UK ISDN lines usually come with two, 64kbps channels. But the growth of ADSL, cable and fibre broadband has almost wiped out the demand for ISDN as a way of accessing the internet.

In the UK, the technology is now largely used for business phone lines, or as a niche product in fields such as radio. As a result, it can be hard to order and install new ISDN circuits.

This, in turn, has prompted broadcasters to look at alternatives. Satellite has always been an option for reporting from the field, using a satellite truck or radio car.

Newer, more portable systems are now widely used by the BBC, and other news organisations, for both audio and video reporting from location. But the relatively high cost of satellite bandwidth means it is not always a practical option.

Broadcasters, then, have followed the lead of other businesses, and investigated the use of IP-based audio links. Plenty of programmes now include contributions recorded over Skype. Some radio stations have taking phone-in interviews over general-purpose IP phones. And specialist providers such as Tie-Line, Comrex and Prodys have developed IP-based audio codecs which connect together studios, or studios and guests, over IP.

These systems are not, though, cheap. A general-purpose IP codec costs from around £2,000 or $3,000. As a result, Comrex and Tieline have developed cheaper, software-based codecs for the remote contributor.

Luci Live, a software-only codec (typically feeding audio into a Comrex Access or other hardware unit in the studio) is now used by the BBC, especially in more remote regions.

An even cheaper option, though, is the new IP DTL service. Developed by media company In:Quality, IP DTL runs in the “cloud”, with both the contributor and the studio needing only a browser – and, of course, a mic, for a quality connection.

Unlike ISDN or satellite, there are no usage charges, just a range of annual fee plans, starting at £34 for charities or £49 for a Podcast account, and ranging up to the National option, with 10 studio log-ins and 100 remote connections. All the paid plans give up to 72kbps bandwidth (slightly more than ISDN), except for the Voiceover plan, which runs at up to 128kbps. We tested the VO plan, running at 64kbps to ensure a fair comparison with ISDN.

There is also a free plan, which comes with one studio and one remote log-in, and 40kbps audio. This lacks the relay servers included with the main plans, but is a good way to test out the technology.

Next: Setting up IP DTL