FORUMS: list search recent posts

Trying to eliminate bad hiss per a wireless boom setup

COW Forums : Audio Professionals

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Seth Diamond
Trying to eliminate bad hiss per a wireless boom setup
on Nov 8, 2017 at 12:09:33 am

Hey everyone,

Here's the scoop. I'm having a terrible time trying eliminate really bad hiss (a truly unacceptable noise floor) per a wireless boom setup that I’m assembling. What I have right now theoretically should work, but the hiss renders the sound capture totally unusable. Maybe it’s a simple fix that just involves adding an inline RF filter somewhere?

The signal chain is as following:

Audio Technica AT4053b (boom for indoor voice) ***OR*** Audio Technica AT875b (short shotgun for outdoors) ---(8” XLR patch cable)--->
Sennheiser MZA14 48 (supplies +48V phantom power to either mic) ---(8” XLR patch cable)--->
Sennheiser EW100 G3 wireless microphone XLR transmitter —(WIRELESS CONNECTION)--->
Sennheiser EW100 G3 wireless receiver —(3.5” headphone jack to XLR)--->
Sony FS7 (line in)

Again, what I hear is clearly a hiss and not a hum or a rumble.
There is is no AC power involved in the system, let alone an earth ground anywhere.
In some cases, I can attenuate the hiss by holding the MZA14 and the EW100 transmitter boxes differently (I guess I’m the ground in that case?).
But then, once I have the noise quieted a bit, sometimes I hear music in the background - which sounds like pop music that you wouldn’t typically hear on AM radio these days.
When I let go, or change the position, the hiss comes back in full force.

Per the Sennheiser EW100, I have played with the squelch, sensitivity, changing channels, and even dropping the preamps on the FS7. No luck.
Again, it seems to have something to do with there not being an earth ground involved.

Per testing individual components in order to rule things out, the signal is totally quiet when:

* Either mic is directly connected to the FS7 just via a simple XLR cable (with +48V provided by the FS7
* Either mic is directly connected to the FS7 via an XLR cable and just the MZA14 (with +48V provided by the MZA14)
* The EW100 system is used without the MZA14 in the chain (such as with an MD46 mic that doesn’t require +48V or an EW100 G3 wireless lav transmitter)

Per my research, I thought a “ground lift” (eliminating ground pin 1) might eliminate the hiss - but that seems to be for ground loop issues - meaning hums and not hisses. I haven't tried it, but I'm guessing it won't work.

Any thoughts? Thanks in advance!

- Seth


Return to posts index

Richard Crowley
Re: Trying to eliminate bad hiss per a wireless boom setup
on Nov 8, 2017 at 1:44:28 am
Last Edited By Richard Crowley on Nov 8, 2017 at 1:54:43 am

Can we assume that you mean a Sennheiser EK 100 G3 receiver? Can we assume that you mean the "AF OUT" line-level 3.5mm output? There is no headphone jack that I can see?

Most cases of hiss have nothing to do with grounding. And that would appear to be the case here, at least judging by your reported symptoms. Since all parts of the system are battery-operated, there is no ground reference anywhere. And the system does not need any kind of ground to operate properly.

Excellent troubleshooting technique to evaluate each link in the audio chain separately.

Did you hear ANY difference in noise floor on all the various sensitivity settings on the transmitter?
And when you changed the audio level settings on the receiver?
I would have expected obvious changes in the noise floor when you adjust the audio levels.
And you confirmed that it is NOT in squelch (muted)?

Did you try different cables, especially between the mic and the phantom supply, and between the supply and the transmitter?
I didn't see any mention of what you used to connect your XLR output (from the power supply or the MD46 mic) to the transmitter?

It is also not clear from your description whether the problem is that the audio signal level is too LOW, or whether the noise floor is too HIGH. They both produce the same resulting poor signal-to-noise ratio. But the causes (and solutions) are rather different.

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


Return to posts index

Bruce Watson
Re: Trying to eliminate bad hiss per a wireless boom setup
on Nov 8, 2017 at 3:59:17 pm

[Seth Diamond] "Audio Technica AT4053b (boom for indoor voice) ***OR*** Audio Technica AT875b (short shotgun for outdoors) ---(8” XLR patch cable)--->
Sennheiser MZA14 48 (supplies +48V phantom power to either mic) ---(8” XLR patch cable)--->
Sennheiser EW100 G3 wireless microphone XLR transmitter —(WIRELESS CONNECTION)--->
Sennheiser EW100 G3 wireless receiver —(3.5” headphone jack to XLR)--->
Sony FS7 (line in)"


As I said over on Gearslutz, the problem is that you are trying to use the Sennheiser G3 output as line level. You'll have to crank the receiver all the way up to get to the bottom of consumer line level (+4dB professional line level isn't a possibility with the G3). There's some of your hiss. Then you have weak line level at your FS7 so you have to crank up the volume there, and there's the rest of your hiss.

Use the G3 as Sennheiser intended -- as a microphone. So drop the FS7 to mic level input, turn the volume down on the FS7, and use the G3 receiver to carry most of the amplification load to come into the FS7 with a strong mic level signal. If you get your gain staging right you should have substantially less hiss in your recordings.

But the real problem here is you aren't using a mixer. People are practically giving away SD MixPre-Ds on the used markets. Get one and use it, sell off the MZA14. You'll get considerably better sound, less noise (the MixPre-D can easily deliver a pro line level signal to your FS7), much better metering, and first class limiters. The limiters are worth the price of admission by themselves.


Return to posts index


Rob Neidig
Re: Trying to eliminate bad hiss per a wireless boom setup
on Nov 8, 2017 at 9:35:33 pm

It's not clear how you are connecting the AT4053 or AT875 to the Sennheiser transmitter. The stock kits come with a lav mic to connect to the transmitter, and I believe a mini-jack to mini-jack cable for connecting other sources. If you are using different cabling than that, then that could be some of your problem. Even if that is sorted out, then I believe Bruce has the right idea in making sure you are using the correct levels all the way around.

Rob Neidig
R&R Media Productions
Eugene, Oregon


Return to posts index

Seth Diamond
Re: Trying to eliminate bad hiss per a wireless boom setup
on Nov 13, 2017 at 9:34:49 pm

Thanks for the updates so far, everyone! I’ve been away for the past week and away from my gear; I’ll do some more testing now that I’m back. Here’s the update:

@Richard Crowley – Yes. It’s a Sennheiser EK100 G3 receiver, and an SKP100 G3 transmitter. The AF OUT line-level is what I meant. Thanks for the positive support! I have definitely played with the sensitivity settings/preamp on the FS7/squelch settings/different cables. The MD46 is a dynamic (and unpowered) mic, so it didn’t need an XLR cable there. I’m getting plenty of signal, so it seems like it’s a high noise floor issue. More on all this in a bit.

@BruceWatson – Thank you so much for both your replies here and on Gearslutz, Bruce! I really appreciate it. Per the hiss, this definitely seems to be some sort of an RF thing going on here instead of mismatched levels; read below to see what I mean. (Meanwhile, there’s no argument from me about getting the levels right – but something is definitely causing ridiculous noise where the hiss is as loud as the mic input – not something more subtle like background hiss from inexpensive preamps.) Trust me – I’d Love (with a capital L) an SD MixPre-D if I could snag one at about $350 on eBay, but unfortunately it’s not an option right now. I spent my next-to-bottom dollar to get my hands on a used AT4053b (rare as hen’s teeth as used) and was lucky to get my hands on the MZA14 for stupidly cheap when I realized that my SKP100 didn’t provide +48V phantom power. It’s on my wish-list, to be sure!

@RobNeidig – Sorry for not being clear. The mics go into the SKP 100 (not a EW100 transmitter), but it transmits to the EW100 receiver. Sorry about the confusion. Please see what I wrote above per Bruce.

*********************


Here’s an update after a bunch of testing this afternoon, which will hopefully help rule things out. It looks like I have two separate problems here:


(1) RF SPRAY FROM THE SKP100 TRANSMITTER?: Check out the following picture of my setup. When I hold the SKP100 just like this, with my three fingers fully wrapped around the XLR connection and with the palm around the body of the SKP100 transmitter, almost all the noise goes away. Can I put something in there (ferrite RF chokes?) to shut down what may be RF Spray?

I’ve pulled the mics themselves out of the equation; the noise happens regardless of whether a mic is connected to the chain. Stripped down, it happens when the MZA14 is directly connected to the SKP100.


(2) FM RADIO INTERFERENCE: Once I hold the grip that way, most of the noise is gone. But in certain circumstances I’m now picking up variably slight broadcast radio noise. What’s weird is that I am in fact picking up FM (not AM) signals. At its worst, the sound is a couple of FM stations playing all at once. The clearest of the radio station signals is WBMX 104.1 FM, which is a powerful FM radio station (21,000 watts) broadcasting from the Prudential Tower exactly two miles away.


By the way, as far as cable quality goes, I’m planning to return the brand new 8” one (shiny cable ends) to Amazon -- but neither cable seems to do anything to significantly solve the main hiss problem. I think the coiled black cable (Pearstone, with Neutrik ends) picks up less of the lower FM signal, but there’s higher handling noise when the coil moves around – so I’ll likely have to replace both cables for this application.

Thanks again in advance!



Return to posts index

Seth Diamond
Re: Trying to eliminate bad hiss per a wireless boom setup
on Nov 14, 2017 at 4:28:42 pm

I'm tentatively optimistic here! With a test of effectively disconnecting Pin 1 (by jumping the Pin 2 and Pin 3 pairs respectively -- but not Pin 1) between the MZA14 and the SKP100, I think I created a ground lift - which has quieted things down. As the mic works, the +48 phantom power is in fact being passed through.

Would a solution of using a transformer instead of a ground lift do the same thing here? Would that be a quieter solution than a ground lift?

Assuming I just go pick up a ground lift (as a permanent solution to the first problem here), I now need to get rid of the rest of the hiss and FM signals that I'm picking up. Any thoughts? What's the next step?


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2018 CreativeCOW.net All Rights Reserved
[TOP]