Reporter's Notebook

The art and science of the interview

Posts Tagged ‘mix-minus

Gear 2.0

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Mixer and Inline Patch Setup

I’ve written about gear and gear related frustrations before here, here, here, and here.  I’ve been through three mixers, two phone patches, a half dozen visits by the phone company and a number of wiring configurations on the way to where I finally am today.  That place is interviewing happy land.  Through two years of trial and error, I’ve reached a point where the telephone interviews I conduct (1) have no line noise, (2) can be heard by the person I’m talking to, (3) have audio levels between us that are balanced and (4) uses a setup configuration that makes sense.  If you’re doing telephone interviews, each of these is important but radically different from the other.  I’ve found lots of stuff online that was, to some extent, helpful.  So I want to give some advice and some help back.

(1) No line noise means just that.  I think when most people use the phone, they only notice line noise like scratching or hum when its obvious.  But when you’re doing interviews and there are moments when the guest is responding to a question, there can be long seconds of silence.  That is where you’ll hear even the quietest hum and that is the sign of a substandard setup.  Hum can be caused by transformers too close to gear inside the house.  But make sure you have the phone company check the wiring and the line to make sure it isn’t them.  A shorted wire can cause it.  Maybe your old 4-strand wiring needs to be replaced with Cat-5 or higher wiring.  Also some lines are just noisy and you can ask the phone company to install on your line an industrial version of the little transformer that is at the end of many older USB cables.

(2) Being heard by the other person has a lot to do with how well the telephone patch separates your voice from who you’re talking to.  I’m no expert at this, but I’ve learned that before a mixer can do you any good, meaning before you can put your voice on one channel and the caller’s voice on another, the phone patch has to split them.  It does this with something called a digital hybrid circuit.  And once the call gets to your mixer, the mixer has to employ something called mix minus, meaning your own voice doesn’t get fed back to the line.  If it does, it gets cancelled and that can contribute to the third problem, equal audio levels.

(3) I can’t tell you how many times I’ve had an interviewee tell me they can’t hear me very well.  I sound like I’m far away.  I sound like I’m in a box.  This is because digital hybrids also differ in how loud each side of the call (caller v called) is.  Most have a 20db difference between the two, meaning the caller is going to be louder than you going into the mixer.  And even if the hybrid has split the call and the mixer has each side on a different channel, the mixer can’t compensate for the difference.  You have to have a hybrid that lets you control levels on both sides of the call so you can adjust them manually.  For reference, an increase of 3db means the audio just doubled in intensity.  So imagine how quiet a reduction of 20db can be.

(4) The mixer I started with was tiny.  It didn’t have a lot of the extra jacks I needed to give me the flexibility to control aspects of the call.  The next mixer had more jacks, but honestly, I didn’t know how to use them.  And let me tell you, looking for help either online or in gear stores was futile experience.  Audio stores like, for instance, Guitar Center, know mixers for recording bands.  They know nothing about configurations for broadcast, podcast or telephone interviews.  So when I showed them a block diagram I drew as a way to try to understand why my interviews were so poor, they couldn’t help.  After months and months of switchiing out gear and switching around cables, I finally stumbled upon a setup that works perfectly.  And that also means I don’t have three or four sliders up or a handful of pots turned in crazy ways.  I took a picture of the setup so I can never screw it up.

Now, for the help. If you’re doing telephone interviews for broadcast or podcast, I’ve discovered there are lots of ways to record phone calls.  The easiest seems to be with Google Voice.  Then, there are a number of digital plug ins you can use with mobile devices.  Me, I think the Plain Old Telephone System is going to be around for a little while longer, and since I’m not that enamoured with VOIP, I’m sticking with analog.  So, if you are too, here’s what I’m using:

– JK Audio Telephone Inline Patch (Less expensive than the Broadcast Host and does almost everything BH does for $200 less. Has 40db rather than 20db separation.  Apparently, more is better).
– PROFX8 Mixer with USB
– Shure SM7B Microphone

But the most valuable thing you need is someone to tell you if you setup works before you’re on the line with an important interviewee who can’t hear you.  That means you need a caller to call.  But I can tell you people get annoyed quick if you call them over and over and over, which is what you need to do the test your gear and check your setup.  So, I suggest you use something called “Tell Me” (408-752-8052).  Tell Me is a voice activated service that can deliver sports, weather, news and much more over the phone.  It works by voice command.  And because it works by voice command, that means it knows what a voice at proper volume should sound like.  So you can call it to check your system.  Talk through your microphone, through your mixer, through your phone patch, to Tell Me.  If something is wrong, you’ll figure it out quickly.  It’s not a free service, but its per-minute rate is not overly expensive.

And even though, as I said earlier, there isn’t much online that can help (even many of the YouTube videos weren’t specific enough), this instruction sheet from BSW was helpful –

I’m glad to say I think this is my last post about gear problems for awhile.  Yaaaaay!

Better Gear; Better Life

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I posted about a Behringer mixer I bought earlier this year that I thought would meet my needs. When I talked about the smaller Xenyx 502, I was happy with the construction of the box, the clean signal with no noise, and the simplicity. But what I didn’t realize when using an analog mixer (which is slowly going out of fashion it seem in favor of digital mixers), with an analog telephone auto hybrid (digital versions of these are also touted to be better), the problem is feedback. I’m not an engineer, and believe me, I’ve posted to audio websites and harassed engineers in person and over the phone to try to help me thresh this out.

But in a nutshell, the issue is when the audio comes into the auto hybrid, which is a box that turns the telephone signal into something the mixer can hear, and is then fed into the mixer, the 502 didn’t prevent the signal from seeing itself. Somehow, and I don’t know how exactly, the voice coming in collided with the voice going out within the mixer and so, when caller audio passed through the auto hybrid on the way back to the caller’s earpiece, there seemed to be two problems. First, that collision seemed to cause the microphone I’m using to drop so low that the caller couldn’t hear me. Second, because the caller’s incoming audio and the microphone audio were somehow intermingled, when I tried to boost the caller’s audio if it got too low, there would be massive feedback. Likewise if I tried to boost my audio, the microphone was terribly distorted and the audio was garbage. I’m sure part of the problem too was that the 502 allowed me to input my audio only through LINE IN inputs and hear my audio from MAIN OUT outputs.

The Xenyx 802 apparently solves that problem with two different sets of jacks connected by a process. The jacks, FX SEND and STEREO AUX RETURN let me feed the auto hybrid’s input to the former and output the caller’s audio through the latter. The process in-between is something called “Mix Minus”. This, apparently, returns all of the sound the mixer hears to the auto hybrid except the caller audio. These advancements, something the 502 didn’t have, eliminated feedback and separated the microphone and the telephone line. I now have full control over the caller audio and can boost it without feedback. Likewise, I can increase microphone levels if I need to and now, the caller can hear me with no problem.

This problem, as readers of my blog know, has dogged me for months. It now seems solved. I have to say how much I appreciate all of the people who listened to my problems. In the end though, I was the one who understood the uniqueness of the problem and I was the one who had to research how to fix it. That isn’t to say nobody else helped, but it wasn’t their problem and bottom line, they had their own stuff. That’s the thing about fixing problems. In the end, they’re ultimately yours to abandon, live with or solve. Of course, for anybody else with this problem, I’m glad to gallop to the rescue.

Written by Interviewer

September 18, 2013 at 21:36