Recording telephone calls for podcasts and broadcasts

Telephone interviews are tricky things to record. It makes life a lot easier if all the presenters can hear what the interviewee is saying. In order to do that, you need some way to take the audio from the telephone line and connect it to the mixer. From there it can be sent to everyone’s headphones. It also helps if everyone can ask the interviewee questions quickly and easily. That means sending the audio from everyone’s microphones and sending it back down the telephone line.

Connecting the audio from the telephone line to the mixer is fairly straight forward: Just connect it to a spare channel on the mixer. However, you can’t just connect a spare output from the mixer back into the telephone line now, otherwise the interviewee will hear their own voice coming back down the line at them! This is where you need a mixer with auxiliary outputs like the Soundcraft EPM12. By connecting one of the auxiliary outputs from the mixer to the telephone line and turning up the auxiliary knobs for each of the presenters’ microphones we send the audio from the studio down the telephone line to the interviewee without sending them their own voice too.

So, how is the telephone line connected to the mixer? We’ve tried a couple of different ways in the past, but currently we use a D&R Telephone Hybrid-2 (sometimes called a telephone balance unit) to provide an interface between the telephone line and the mixing desk. These are expensive bits of kit, but provide the best quality connection between the mixer and the telephone line. They are designed to cut out echo and line noise and generally make the audio presentable. To supplement the hybrid, we use just about the most basic telephone handset available, the BT Décor 1100. The phone handset is necessary in order to make any outgoing calls as the hybrid doesn’t have a number pad. The Décor 1100 is a good choice because it has fairly large numbers which are easy to stab a finger at and has an LED on the top which flashes when the phone rings. This means you can turn the ringer off on the phone (useful in broadcast environment) and still tell when someone is calling you! The quality of the telephone handset doesn’t affect the quality of the recording: All the audio is diverted from the handset when the hybrid is active.

A much cheaper way to record telephone conversations for broadcast is to use a telephone recording adapter. This particular model connects into your telephone socket with an adapter so you will all have to share the telephone handset in order to speak to the interviewee! Other similar devices work by being connected between the base of the telephone and the handset itself, which means you need a telephone which has a detachable handset. Fortunately lots do, including the Décor 1100. Devices which work in this way have the advantage that you can all hear the caller via your headphones and the caller can hear you all via the microphones.

All of these methods are dependent on the quality of your telephone line and the connection to the interviewee. It is better for reliability and quality if they are on a land line rather than a mobile. One way to get a good quality recording regardless of the quality of the telephone line, is if the interviewee is able to record their side of the conversation and send it to us so we can mix it all together afterwards. Then it sounds like we were sitting in the same room as our interviewee when we spoke to them.

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    5 Responses to Recording telephone calls for podcasts and broadcasts

    1. Tony,

      Thanks for the great tips on audio gear. I can easily see myself shelling out for some of these gadgets.

      I have only done a small amount of interview recording for IBM internal use. I may have lower standards with regard to sound quality, but I found that it was actually better to record interviews via the phone than in person because if for example the interviewee was not near enough to their microphone this would be immediately obvious to me if I was interviewing by phone, while if I was doing a face-2-face interview I wouldn’t realise the problem until I played back the recording.

      I have experimented with several tools, but the easiest to use is Skype-call-recorder (see the recording software is open source even if Skype is evil. The two ends of the call are automatically recoded as left and right channels in the stereo recording so it is easy to adjust for relative loudness of the two voices later.


    2. Tony says:

      Thanks for the tip Brian! On the Ubuntu Podcast we avoid non-Free Software like Skype as we try to show that we can do anything with Ubuntu! That said, there are plenty of podcasts out there who use Skype and that tool or similar.

      In regards to face-to-face interviews, plugging a set of headphones into your recording device is a great way to monitor the levels. Also, a lot of hand-held recording devices (like the H4n mentioned above) have visual displays which help reassure you that you’re getting a good level too.

    3. Ken says:


      I designed a telephone answering machine which separates both sides of the conversation and records to flash memory. I can easily strip off the analogue at sensible recording levels to feed into a mixer. I could re-purpose a unit and send it your way.

      BTW – thanks v.much for organising OggCamp – should have some cool stuff to present there. Aug 14th is my 40-somethingth birthday – so double celebration.


    4. Tony says:

      Hi Ken,

      Thanks for the comment. I guess you meant ? I’d be happy to road test your device if you could rig one to have input and output ports. 🙂

      Looking forward to seeing your stuff at OggCamp, I’m sure it’s going to rock!