Weird noise coming in on voice recording - how to remove?

M

Movie_Dude_3

Well-known member
Here is a snippet of an audio recording captured today: https://www.dropbox.com/s/2eyqoocnjh8qbsq/Weird Sound.mp3?dl=0

This was recorded with a pair of Sennheiser G3s routed to a Tascam DR-40.

There's room tone - sounds like air - that rises and drops in volume along with the speaker's voice. I tried different levels of Low Cut on the field and it didn't remove the sound. In post, I used "Capture Sound Print" and "Remove Sound" in Audition - no luck (I had recorded 15 seconds of just room tone). Adaptive Noise Reduction in Premiere didn't work.

Any idea what this might be, and how I can remove it in post? And how I can I avoid this in the future?
 
Just out of curiosity, did you properly gain-stage everything in the chain? Transmitter, receiver, and recorder? How hot was the signal in the transmitters?
 
Alex H. said:
Just out of curiosity, did you properly gain-stage everything in the chain? Transmitter, receiver, and recorder? How hot was the signal in the transmitters?
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Not hot in the transmitter, receiver, or the recorder. Everything looked normal, no peaking. The highest it peaked in the original recording was - 9db, so I added gain in post.
 
Sounds like a bit of distortion along with some heavy gating. I'm not really familiar with the DR-40, but think in general Tascam makes decent stuff. Did you have an Automatic Gain Control (AGC) or Auto Level feature engaged? I think there's like a "feature for recording a lecture" setting that "ensures" you don't get heavy clipping or really quiet passages, but at the expense of audio fidelity.

Not sure exactly what to recommend (since Alex already pointed to gain staging). Maybe you can gather some tips from this review? I just skimmed it, but the writer, Jeff Towne, knows what he's talking about.
https://transom.org/2011/tascam-dr-40/
 
Jim Feeley said:
Sounds like a bit of distortion along with some heavy gating. I'm not really familiar with the DR-40, but think in general Tascam makes decent stuff. Did you have an Automatic Gain Control (AGC) or Auto Level feature engaged?
Click to expand...

This is what my initial thought was also. Sounds like a poor example of AGC that's gating and distorting.

DR-40 should do better than this, so I'm not sure where it's coming from. I'm also doubtful of this coming from the Sennheiser G3s; I've never had sound like that from my own Sennheiser G3s. So... I'm lost. I don't know what to suggest, other than careful gain staging and proper mic placement.

As to fixing it in post... if you could, it would probably be way more work than it would be worth to me. Fixing gating issues is a PITA, and a few seconds of it in a recording takes me hours of work in the DAW, all for mediocre results. Seems like cruel and unusual punishment.
 
Movie_Dude_3 said:
Not hot in the transmitter, receiver, or the recorder.
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But how hot, especially in the transmitter? What’s your AF Out level setting on the receiver, and how much gain did you have to add in the DR-40?

I ask because this sound is not uncommon when the audio level is low in the transmitter. I’ve heard it in systems from other brands as well. Low transmitter gain can be adversely affected in a wireless processing and signal chain. I use G3 systems often and don’t have these issues, but I’ll try to see if I can recreate yoir issue tomorrow. Were you using the stock lav, or something else?
 
It sounds like companding artifacts from the radio mics and could even be the two of them interacting if their frequencies are summing on second and third harmonics that is potentially producing a third frequency interfering.

Try different frequencies on one of the radio mics and see if it improves. It may also be worth checking that the TX and RX are exactly on the same frequency as slight de-tuning would still give a signal but cause the same artifacts.

The sennheiser RF guide is well worth finding as it explains how radio mics can interact with each other to cause problems.
 
Alex H. said:
But how hot, especially in the transmitter? What’s your AF Out level setting on the receiver, and how much gain did you have to add in the DR-40?

I ask because this sound is not uncommon when the audio level is low in the transmitter. I’ve heard it in systems from other brands as well. Low transmitter gain can be adversely affected in a wireless processing and signal chain. I use G3 systems often and don’t have these issues, but I’ll try to see if I can recreate yoir issue tomorrow. Were you using the stock lav, or something else?
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AF out was -6 dB, no gain added to the DR-40 (set to 0). I used the stock lav.

Should the AF out be higher than it is?
 
GaryNattrass said:
It sounds like companding artifacts from the radio mics and could even be the two of them interacting if their frequencies are summing on second and third harmonics that is potentially producing a third frequency interfering.

Try different frequencies on one of the radio mics and see if it improves. It may also be worth checking that the TX and RX are exactly on the same frequency as slight de-tuning would still give a signal but cause the same artifacts.

The sennheiser RF guide is well worth finding as it explains how radio mics can interact with each other to cause problems.
Click to expand...

I'll have to check out the RF guide. Thanks for the tip!
 
I replicated all my settings here in the office and I'm not getting the same results. I'll keep messing around but that's what I have so far.
 
It sounds to me like intermod distortion - although quite mild. The impact of two frequencies in use that are incompatible. It's usually much worse than that, but it does have that strange characteristic where the intermod gets worse on speech peaks as the deviation increases.

Can you re-create it, and if you can, turn off the other transmitter. Remember that Sennheisers can transmit on any frequency in their range, but performance of multiple units requires the frequencies chosen to play well with each other. Generally the frequencies in the banks are selected to minimise the interference, but if either is on a random frequency, even quite a way away, then intermod is possible. Many people just check two radio packs are on different frequencies, and assume this works. It doesn't.
 
paulears said:
It sounds to me like intermod distortion - although quite mild. The impact of two frequencies in use that are incompatible. It's usually much worse than that, but it does have that strange characteristic where the intermod gets worse on speech peaks as the deviation increases.

Can you re-create it, and if you can, turn off the other transmitter. Remember that Sennheisers can transmit on any frequency in their range, but performance of multiple units requires the frequencies chosen to play well with each other. Generally the frequencies in the banks are selected to minimise the interference, but if either is on a random frequency, even quite a way away, then intermod is possible. Many people just check two radio packs are on different frequencies, and assume this works. It doesn't.
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What if I only had one transmitter?
 
The compander in the G3 can be audible with low input levels on the Tx. in addition you could try another preset bank. As was stated, presets within the same bank should not have any intermodualation issues but third party interference is always possible.
I've never had issues with my DR-40, but I've never used the auto level mode. (AGC). The 'Peak Reduction' mode works decent though but it's not a typical AGC continuous variable gain. A limiter can be also be enabled in mic level mode which probably could produce some unpleasantness if hit hard. The DR-40 also has a low-res MP3 mode which could produce some artifacts in the 32 or 64 kbs mode as well as FX and a MS decode mode on record and/or playback.
 
Other external RF sources could also affect the G3 transmission so it may just be a one off or sometimes some people just absorb RF and can be difficult to use radio mics with.

Even with our high end sennheiser analogue and digital radio mics at work we can get unexplained drop outs inside studios that are shielded from the outside world.
 
Movie_Dude_3 said:
I replicated all my settings here in the office and I'm not getting the same results. I'll keep messing around but that's what I have so far.
Click to expand...

Using both systems? If it is frequency intermod, running a single system won’t replicate the issue.
 
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