Noise/hiss with external mic only (Azden SMX-10)

Some follow-up. I was going to return the SMX-10, but there was no way I would get a replacement in time, even if I knew what to get, so I held on to it. First, I tried it outdoors in a very quiet environment. I recorded some birds, a woodpecker going at a tree, and nothing at all - just to see if there was noise. It seemed OK. Rather than "much worse than the built-in mic", it seemed better - nicer tones, maybe a little more noise.

So I took it along to this event and recorded about 5 minutes of a speech before an audience. The audio wasn't bad. The mic picked up a lot more side noise than I would have liked, from people around me before they quieted down - "shotgun" is a nice term, but of course it isn't really like that. Further on, I got some weird interference sounds which I think I recognize as a GSM phone talking to a tower - I've heard this if I have an AM or shortwave radio on near my cell phone (on but not in use), but I don't know why the camera or mic would pick it up (it isn't audible). After that, the audio was fine.

So now I'm not sure what to do. I'm thinking of called Azden to ask about the SMX-20, which is a newer model that says it was "designed for DSLRs". The specs don't look much different to me, and it is so new it doesn't have reviews, but I would like to hear what they say about it.

So your "cell phone noise" isn't actually audible. It is an interference that likes to hit the cables and is picked up that way. Some cables are more shielded than others. I get that sound on my boom mic sometimes if I have my cell phone in my front right pocket. That's the side I have my 6ft, coiled cable running out of my sound bag to my internally cabled K-Tek boom pole. It's generally not a problem as long as I keep my cell phone away from that cable. If it gets too near, the boom cable can get hit with it. It's not just GSM phones, but all higher powered "smart" phones like the iPhone, BlackBerry, Droids and many others. It's usually fixed with a proximity fix from the effected cable. Normally I don't have to move my cell phone (HTC Amaze 4G) too far away before that sound doesn't effect anything. But on some cheaper, less shielded cables the effect could be even greater. The cable I'm talking about can be stretched out to be 6 ft. in length, but it is shielded. Its basically a very long antenna of sorts. A shorter 12" cable could even be hit if it wasn't shielded at all. A lot of consumer grade XLR cables use cheaper cable and connector bits. The expensive Mogami cable and Neutrik connectors are better at shielding from that interference.

lar55 wrote in post #14053481
Further on, I got some weird interference sounds which I think I recognize as a GSM phone talking to a tower - I've heard this if I have an AM or shortwave radio on near my cell phone (on but not in use), but I don't know why the camera or mic would pick it up (it isn't audible).

What you are picking up is the data stream from the handset communicating back to the base transceiver station (BTS), basically the way the system works is the BTS polls the handset and the handset replies back during it’s assigned time slot, and those series of data bursts from the handset are entering the cord of the Azden SMX-10 and are being demodulated by the electronics in the camera body, the problem is exacerbated by the fact the Azden SMX-10 utilizes a consumer style un-balanced cable (two wire one hot one shield return or in the case of stereo two hots and a single shield return), which is considerably more prone to external interference than a professional balanced cable utilizing metallic XLR connectors.

This is prime reason you will always want to keep un-balanced cabling as short as possible and whenever possible as far away from cellphones two-way radios etc. as you can.

For what it is worth, balanced audio cabling is the only acceptable method of wiring in high radio frequency environments, which is why from the lowly 1 Kw Harris transmitter up to a blow torch 50 Kw Nautel, one will only find balanced audio inputs being utilized.

Now balanced audio cabling can, under certain circumstances, pick up this type of interference, but in most cases the problem can be traced back to poor shielding in the cable, such as found in ultra-flex microphone cables which lack a full metallic shield, plastic shelled XLR connectors, or poor or failed bonding to a metallic XLR connector shell, or an impedance mismatch between the devices connected to each end of the cable.

Wayne