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HDVoice In Service Of Online Radio: Part 2

In part 1 I addressed Soljon’s question about how to physically connect a G.722 capable SIP phone to a traditional audio mixer for use in an online radio project.

I understand and appreciate the intention to use a phone as the audio interface device. Phones are effectively appliances, offering excellent audio quality combined with simplicity of operation and high reliability.

This very logic leads me to use my Polycom IP650 in some unusual ways. For example, when I occasionally guest host the VUC calls I will call the ZipDX wideband conference bridge on one line, then call the Talkshoe G.711 bridge on a second line and perform an on-phone conference to connect the two bridges. Finally I engage the call recording function on the IP650 to give me an uncompressed WAV recording of the entire call.

The uncompressed recording of the call is more convenient for post-production purposes. I usually prefer to work in the uncompressed domain, then create a final MP3 for release as podcast as the last step in the post-production process.

In these instances I don’t join the VUC call using the Polycom phone. I usually join the call using Eyebeam and a cordless headset. This gives me some independence. I can drop off the call and know that the bridges are still joined and the local recording is continuing.

For Soljon’s situation soft phones offer some flexibility that a hard phone may not deliver. There’s a second wholly different approach that you might take based upon using a soft phone and connecting the host computer to your mixer.

To do this you’ll need some kind of audio capability on the host computer. There are myriad ways to get audio in/out of a computer, some cheap and some very costly. If the host computer doesn’t have audio capability you can always add it by way of a $10 USB sound adapter (pictured above.) I’ve frequently used such simple hardware to record screencast tutorials with voice annotations. They can sound surprisingly good, certainly as good as a G.722 encoded phone call.

The weakest aspect of such cheap audio interfaces is the microphone preamp. However, on our example application we don’t even need the mic preamp, so the cheapo adapter will work just fine.

Unlike in earlier years, there are now numerous soft phones that support G.722 based wideband audio. Here’s a list just off the top of my head:

While there have been issues with faulty or incompatible G.722 implementations these are becoming less common as over time there is more and more real-world G.722-based interop happening. Even so, you should test the soft phone you select to ensure that it works well with your chosen conference bridge and hardware phones.

Given that a soft phone will use whatever audio interface you have on the host platform it should be no more difficult to connect it to the mixer than a hard phone. Most likely a 3.5mm to RCA or 1/4″ TRS cable is all you need.

Soft phones tend to be relatively light applications which means that you can pick a low-cost host platform like a netbook or net-top and treat it like an appliance. You may even select a thin client or embedded PC as I described recently when discussing DIY Asterisk Appliances.

I have used Eyebeam and PhonerLite on my HP 2140 and 5102 netbooks and not had a problem as long as that was the only app that I was running at the time.

Netbooks are nice as platform because they are cheap, small and include a keyboard, monitor and mouse built-in. That means that once you have the call up and running you can place them safely out of the way and go about the business of the call.

As I described previously, the most ideal production circumstance may not be the obvious one with respect to the host. You really want to the host to be primarily engaged in the conference call using some kind of phone. Then take an audio feed from the conference call into the production mixer.

This simplifies that audio handling process considerably since you don’t need to feed the output of the mixer into the conference call. This reduces the likelihood of echo and feedback on the call, albeit at the cost of degrading the hosts audio to that of the conference call itself.

The conference bridge has the ability to send each participant what is known in music as a “mix minus” feed. That is, each person hears others on the call, but not themselves. When you try to include the production audio mixer into the call in both directions (sending and receiving audio) this becomes much more complicated to do.

If the soft phone is merely being used to pass the call audio into the production path then you can simply mute the mic on the soft phone secure in the knowledge that it will not introduce noise into the call or the program audio. Many soft phones will also record the call giving you a backup local recording for possible use in post-production.

At every turn down this path I seem to discover slightly different and potentially advantageous way of doing things. So, believe it to not, there will be a part three to this little series. In part three I will look at some unusual ways to leverage soft phones that you probably would not have considered.

This Post Has 7 Comments
  1. My Suggestion:
    The hardware I want to offer as a suggestion for hooking into a radio system might be at the upper end of a person’s budget, but I wanted to put it out there. The Polycom Soundstation IP 7000 with the Multi-Interface Module (Together about $1000). The extra module acts as PoE device to the phone, as well as a 4 port network switch (one dedicated to the phone connection), and has Stereo RCA Input and Output jacks (at typical line-in and line-out levels, as far as I can tell). This setup seems to be very well suited for a very large conference room where you might use a PA or large speakers for the audience, as well as a wireless mic for the presenter(s). But this would be a very good solution for hooking into an audio board for a radio broadcast. When using the phone in this mode, the added mic becomes part of the phone’s mic array complete with gating the proper mics (it would be great if I could completely shut down the phone’s mics when I want, it may be possible, but I haven’t looked into it).

    Quick Start Guide:

    I purchased this setup with the intent of adding a wireless lapel mic to the phone for our presenters to wear in a large conference room (25′ x 25′). But I am having trouble picking out a proper lapel mic in the $100-$150 range that will have adequate audio level so as to not need a pre-amp (a standard microphone’s output is too low to work properly and would need to be boosted). If you, Michael (or any reader) has a suggestion of a lapel (lavaliere) mic that they have used that has an adjustable audio level, I’d appreciate it.

    1. That’s a nice solution, if pricey. We have the IP6000 in our conference room and love it.

      For trade shows we tend to use the Countryman E6 head worn mics, but they come in the lavalier form factor as well. These are very good kit, and run in the $300+ range for the mic alone.

      Most lav’s are omnidirectional so you need to be careful about getting them sufficiently close to the sounds source that you don’t need a lot of extra gain. The head-worn mics are great since they come right around to the corner of the mouth.

      In television production you often see lav’s pinned to the lapel. That presumes that there’s little sounds reinforcement going on. it’s sufficient for natural pickup of the voice for broadcast, but often too distant from the mouth if the environment is noisy.

      Lav’s generally need some kind of power. A wireless belt pack will usually supply the power. Or you can use a “phantom power” insertor if you’re running them straight into a mixer.

      Samson make some nice wireless mic systems for music & presentation applications. Some use the Countryman mics. Some are fairly inexpensive, too.

  2. This is truly excellent information, I am really impressed that you would go to such thorough lengths to write about this scenario complete with photos, testing,etc! I have a lot more to think about now then I did before, thank you!!!

    1. Your application piqued my interest. When in high school I was a radio DJ part time so I have more than one kind of connection to what you’re doing. Plus I have the right sort of gear on-hand, which makes it easy.

      Finally, as my wife would tell you, my specific expertise is in taking things just a little too far, driven by my own curiosity.

  3. Just an update here. I purchased this dual lav wireless mic system from amazon that is made by a company that makes karaoke equipment (Audio 2000).

    The sound quality is pretty close to the quality of the IP7000 mics when making a wideband call. And it has knobs for changing the audio output for each mic, as well as pots on the transmitters to change the sensativity of the mics. Works great in this system. Far as I’m concerned, it’s great audio quality for the price of $125.

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