Saturday, June 28, 2014

Handy Phone Recording Rig Improves Webinar Audio


Sometimes high fidelity takes a back seat to content. In this case, a company that does a webinar series asked for my help in cleaning up and streamlining their audio. I heard their previous webcast and, wow was it bad! Way too much data compression. Intelligibility was suffering. Surely I could do better.

I was asked to record the panelists in different cities in advance of the event, sequence their audio with other voice recordings and create a master .wav file that would be the bulk of the presentation. There would be a live Q&A and a pre-recorded good bye. The webinar would run a little less than an hour. I was also hired to be on site for the show to help the producer.

There are lots of ways to get audio off a phone line. Perhaps the easiest is a phone hybrid and I just happened to have a JK AutoHybrid in my bag of tricks. The phone line plugs into the hybrid and although it has XLR in and out, it has no level adjustments.

Between the hybrid and Pro Tools, I put a Sound Devices MixPre-D so that I could adjust levels as needed. I could have used the MixPre-D's USB out to get into the computer, but chose my RME ADI-8 DS A/D converter. It uses ADAT optical to get into my Digidesign DIGI003R.

In this particular situation, my voice would not be heard so I only used the hybrid as a way to grab the phone audio and bring it into the Pro Audio world. I called each interviewee first to make sure they had a line that sounded good enough. One was on a cell phone and the audio was pretty messy, but she was able to get to a hard line.

A "hard line", BTW is, historically, a copper connection consisting of an overhead or underground pair of wires that bring the phone service into your home or office. Copper is an expensive, aging infrastructure in the USA. As the lines and insulation deteriorate, water from rain seeps in and compromises the connection. Bugs, birds and squirrels also do their unknowing best to destroy the system. The result is a noisy phone line.

Copper lines have worked well over the years, digging into a bundle of copper cables to find problem pairs and fix them is expensive and time consuming. Where ever possible, copper is being replaced by fiber optic cable. Fiber optic cable offers many advantages, but can also be physically compromised.

While the number of analog conversations coming down a copper pair is normally limited to one single conversation, fiber optic lines with digital audio can accommodate many more. That makes fiber optic delivery more economical for the phone companies once they suck up the cost of replacing the copper. Using data compression, the phone companies can fit even more conversations on the line, but as they increase the number of conversations, the fidelity of each one deteriorates. Think of what happens to CD audio when you make low bit rate mp3 files for your personal music device.

You're also aware of this phenomenon on today's cell phones; mushy, swishy artifacts that sometimes make the conversation difficult or impossible to understand. Although we forget, analog cell phones sounded a lot better. My point here is that, these days, phones that plug into a wall may not be hard lines. In some cases, a good cell phone on a good day may sound better than a bad home or office phone on a bad day. If the problem is not in the telephone instruments themselves, sometimes just hanging up and recalling can result in a better connection because the call will be routed through a different path in the communications maze.

We thought to try SKYPE. I've used it in the past and have been very pleased with the quality of the audio, but unless the user has a headset that allows them to have the mic very close and a headphone to keep the computer audio from getting back into the mic, the results can be ugly. And, not all phone headsets are the same; some sound pretty good, others simply suck. The participants were not phone ranger types so I tried to make things as simple as possible.

After a quick call to each person to determine if the connection was good, I was satisfied that each person's phone would do the job, I made appointments for a short interview; about 20 minutes each. The recordings went off without surprise, but I did have to remember to mute my own phone from the phone handset when I recorded them to keep my voice and any noise out of the track.

After editing, I applied parametric EQ and iZotope RX3 Advanced Noise Reduction and Dereverb. I used Pro Tools' stock 7 band parametric EQ to scrape off any low or high frequency junk and to enhance the voice.

Seven bands provides a lot of sound shaping ability. The interface is quick and intuitive. Sometimes the voice would sound a bit thin. I used the EQ to add some upper bass or low midrange to warm the voice up. If the voice is a bit dull, adding energy around 3 kHz to 6 kHz will bring it back to life and dragging the points around in real time while hearing the changes works very well.

The powerful noise reduction in RX3 pulled some of the various low level noise out of the recording and it also
got rid of a lot of the ringing artifacts you hear on phone audio. Dereverb reduced the echo that frequently accompanies phone audio these days. That echo is pretty tight and at first I didn't really think much about there being an echo. After I inserted the plugin, I was surprised by how much it was taking out, and without further damaging the audio. No, the result was not studio quality, but it was obviously better than what I started with.


I put a compressor followed by a limiter in the Pro Tools two-mix to pack the audio; just enough to make it thick. At that point, I attached my Sound Devices 664 mixer/recorder to my Digidesign DIGI 003R and recorded my mix onto the 664. An odd choice perhaps, but the MacBook and webinar software I was using required external audio coming into a MacBook. The 664 makes a very nice playback device. A bit overkill, perhaps, but very solid. The client was very happy.  

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