WIRELESS NOISE--Zoom H4n & Audio Technica Pro 88W
 

I'm trying to figure out how to use a couple of VHF Pro-88W lav systems with a Zoom H4n.

In trying to troubleshoot/eliminate the noise/isolate the problem, I have been able to establish the following:

1) The noise is a mixture of a very high-pitched noise with a low-pitched static.
2) The noise remains whether I use 1/4" cables or XLR adapters into the Zoom.
3) The noise varies in volume depending on where the wires and components are placed relative to each other, but the noise varies randomly as things are moved about.
4) One receiver/transmitter pair is set to channel "A" and the other set to "B".
5) Whether the transmitter is close to the Zoom or not, the noise continues.
6) I briefly heard a Mexican radio station coming through.
7) The Zoom was plugged into the wall through an extension cord.
8) The lav systems were battery powered.
9) I was not able to isolate the noise to a single mic, receiver/transmitter pair or channel.
10) The noise was NOT present when recording through the Zoom's built in mics.

Thanks very much for your advice and help./

Grasping at straws
 

I'm in urban L.A....could the noise be interference? Meaning...VHF is useless in the city?...

Both receivers on, turn off ONE transmitter (leaving the receiver on for that channel) - do you still have the noise? Does it persist in just one or in both channels? Both transmitters on, turn off ONE receiver - do you have the noise in the remaining receiver? For turn off both the transmitter and the reciever on one channel - does the noise persist in the remaining channel? Both channels on, move the transmitters and receivers with respect to each other. Does the noise vary in VOLUME, in PITCH, or both? I'm suspecting either the signals from the two transmitters are beating with each other, leakage from the internal oscillators in the two receivers in close proximity to each other is leaking into their internal circuitry and beating, or RF interference from a nearby source is getting into the system. Of course, it could just be the nature of the beast with inexpensive consumer units like those. One of the things you pay for as you move up into more professional gear is their more robust designs and better construction that make a system less sensitive to such issues.

@0:00. I recorded myself following these instructions. There are two things that are troublesome--firstly, the static "white" noise, and second, a high pitched noise. Yesterday, the high pitched noise was consistent, like a sine wave, but today it cycles, like a persistent beeping.

> (1)
> Both receivers on, turn off ONE transmitter (leaving the receiver on for that channel) -
> do you still have the noise? Does it persist in just one or in both channels?

@0:11. When I turned off the RIGHT transmitter, the high pitched noise continued. When I turned off the LEFT transmitter, at added a hige amount of noise (at about 0:33 in the mp3).

> (2)
> Both transmitters on, turn off ONE receiver - do you have the noise in the remaining
> receiver?

@0:35. I turned off the RIGHT receiver, and the beeping/cycling noise continued.

> (3)
> For turn off both the transmitter and the reciever on one channel - does the noise
> persist in the remaining channel?

@0:50. With the RIGHT channel off, the beeping continued, but was quieter. With the LEFT channel off, the beeping/cycling noise STOPPED, for some reason.

> (4)
> Both channels on, move the transmitters and receivers with respect to each other.
> Does the noise vary in VOLUME, in PITCH, or both?

@1:29. On this occasion, moving the equipment around didn't seem to have an effect. Yesterday, in another part of the house, it had a huge effect, however.

When you picked up the Zoom, just before the end of your tests, the beeping decreased or stopped, couldn't quite tell which, even as you said "that doesn't seem to do anything."

I hear the beep on the left channel. Reverse the inputs on the zoom used by each transmitter/receiver pair. If you swap the wireless sets so the xmtr/rcvr pair that has been on the left is now on the right, does the beeping swap with it?

Turn off the beeping channel's xmtr/rcvr pair and switch the switch the other channel's units from the frequency they're currently on to the frequency the beeping channel's units have been operating on. Does the beep now appear in that channel? Trying to isolate if it's tied to specific hardware independent of frequency or to the specific frequency the hardware is operating on.

The increased hissing you hear in a channel when you turn its transmitter off is the normal "static" you get from an unsquelched receiver that's not tuned to a signal. I think the low hiss you've been hearing with everything operating is just the normal hiss you'll find in inexpensive electronics in the wireless sets as well as the background in the VHF band, and not in itself indicative of a problem. There are reasons UHF is now the norm and Sennheiser's G2/G3 or similar level of kit is considered the entry level for professional grade work. Many users also report a fairly high noise floor with the H4n so that also may be contributing to the hiss you hear. The beeping is a puzzle however. If you live in an apartment I would almost think it was a neighbor's alarm clock that your ears have tuned out but becomes aparent when listening through your electronics LOL. There's a unit down the hall from mine that eminates a sound almost like that for several hours every morning that is audible in the hallway as I walk past their door. Only thing, if something like that was the source of your beeps, I would expect it to be picked up in both lavs. You don't live near an airport by any chance, do you?

we got a constant (not pulsed) sound like that once into our audio system from PWM (pulse width modulation) light on the camera.
where is the power for the reciever comming from?

the only thing that is odd, other than the usual STUFF with VHF systems is that pulsing noise. Sounds most like a Flash capacitor that is fully charged, with a curcuit topping it off continually. is there a digital camera around there somewhere on ? anything with a zenon flash like a cell phone, or flash unit.
Another devices power curcuit, a switching power supply.

do any Wireless intranet devices keep communication going that way when ideling? A home wireless phone system that is retaining connection with its base by flaggin it?
a wireless mouse/keyboard or presentation device on standby.

the mystery sound :-)

I would send someone out to the "fuseBox" and turn everything in the whole house off, then have them turn things on one at a time, and try to find out when it occurs. then reset all the clocks, and go out and buy a UHF diversity system :-)

Bitching
 

OK...I haven't yet done the testing above.

I took it ten miles away and tested it...the high pitched noise was gone.

Unfortunately, I have to use it here where I live so...unless it's some top secret government project parked in a van that's gonna leave soon, or something...I'm ******.

BTW, *** is it with the people on this board always raving about how great a value Pro-88Ws are?

It doesn't really make sense to me because some of them seem completely credibile, like Douglas Spotted Eagle. Could the included mic be adding noise? I've been using those in anticipation of actually using giant squids. The noise which is apparent on all these recordings is appalling...it makes these lavs seem like toys...

Is it possible to use post software to remove that noise effectively without compromising the final quality? Does the H4n's 96khz/24bit resolution depth help this?

Fischer, it might be a good idea to edit that last post if you can and tone down the unparliamentary language before the mods complain!

Interesting discussion BTW and I hope you get to the bottom of your strange noise. I use a Zoom H2 myself but haven't experienced this.

per CM
 

kthx..I'm aiming twds parliamentary


parliamentary |ˌpärləˈmentərē|
adjective
relating to, enacted by, or suitable for a parliament : parliamentary legislation.

So I don't know anything about the AT Pro-88 but the background noise floor sounds to me like what can be expected for VHF and prosumer electronics. Also the beeping does seem to vary in gain right at the end when you are moving things around, even slightly. I'm sure it's something generating EMF of some kind in your area and either the receivers or recorder (or cables?) don't have adequate shielding. It's just why the expensive stuff is so... expensive.

I can not speak directly about the Pro-88W, because I don't own it. I do have an older Audio-Technica wireless system and on many occasion when I used it at a distance of 50+ feet I've had noise issues, but for close up 3-5ft interviews its fine. I've brought these issues up in another wireless thread but people acted like I didn't know what I was talking about. My solution for long distance mic situations is to record with the H4 unattended and add it back in post. Its not a great solution but for me its better than dealing with static caused by wireless interference.

I'm well aware that people have a predilection against VHF. But, yeah, there are a lot of stories out there saying you can get professional results with the VHF Pro-88Ws, especially if you stay in the range of 10-15 feet or so.

I'm going to get in touch with AT tech support by phone and see what they say...because even if I can get past the high-pitched beeping noise, I'd like to know what they have to say with regards to the noise and what this product is supposed to be able to do.

Please pay only token heed to my following comments and maybe run them past a technician as a prompt for troubleshooting.


This may be way off-target but my sense is that the H4n, itself as a microcomputer, may be transmitting RF noise which may be getting into the VHF receiver via the antenna. Only a strong received signal will suppress it and there may remain almost inaudible traces of it there even in a strong received signal.

The strength of the interference may be influenced by handholding the H4n and the position and direction of the cables from the receiver to the H4n.

Firstly eliminate the VHF mike system as the culprit by monitoring off another known good recording system for noise, then substitute the H4n. If there is noise, the workings of the H4n itself may be the offender.

Try wrapping the H4n inside of cooking foil with the foil touching the shield metal of the XLR sockets but make sure an edge does not fold in and touch any of the pins. If this makes the problem go away, a custom metal carry box with a front opening for the touch controls and holes in the sides to enable plugs, switches etc to be got at may work.

Spurious emissions from the H4n itself may not be enough to cause a direct problem but may beat against other RF interference to create a new interference source which might be why you get good results outdoors.

Try using longer XLR feeder cables from the receiver to the H4n. Try coiling them around a piece of steel pipe to change the wavelength of the shields if these are the means RF is being propagated by the H4n.

In this sense, the cable shields may be aerials transmitting RF which the receiving aerial picks up. The interfence may not be travelling into the receiver circuit via the cables themselves.

If you achieve some improvement, a radiocommunications tech may be able to help you devise a tidier solution.

Hopefully you find the way for there will be others to benefit.

A tech at AT mentioned that they don't recommend using more than one receiver/transmitter together...too much interference...at this point I'm inclined to test that...but also probably just abandon all hope re: Pro-88Ws

yeah. I give up.