Missing frequency on Shure sm7b?

G

Giovanni_roses

New member
Hey everyone, just bought a shure sm7b and in rx, I noticed that there seems to be a missing frequency line in my recordings around 6.8khz. Any idea as to why it may be doing this? Sm7b going into a cloud lifter and then into a rodecaster pro audio interface. Could the sm7b be defective? Thank you!

EDIT: Threw in a few audio samples from different sm7bs from other people and they all do a similar thing around 6khz to 7khz. Very interesting. Guess it's normal?

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I don't have one of those mics, so can't check myself. Looks like an Ozone screenshot, right? Why is it looking like a stereo track, and not just the raw, mono take?

My first thought was it was just a null in the room, perhaps. I mean, I'm not sure what you're recording there, but there's usually not a lot of fundamental content in that 6-7kHz range if that's a vocal track.

If different SM7b mics in different rooms, going through different preamps show the same feature, then it's obvious your mic is not defective. Now, if they're all counterfeit mics from the same factory, could be a different answer.
 
I'll give it a try when I'm in the studio perhaps tomorrow, but what is clear is that perfect black line shows something missing at that precise frequency but mics don't do that. In fact, to get such a narrow notch requires a filter - so that's inductance and capacitance. Mics have gentle too and fro in the frequency response and I've never seen one with a severe notch. If you unplug the mic and swap it for another, does it go? My thoughts turn to the cloud lifter - which does have the potential to do a notch - but this is easily proved if you disconnect it and record the SM7B's output and normalise it. You'll raise the noise floor, but that will reveal a notch even more. My guess is when you remove the cloud lifter the notch will vanish. If it doesn't, then swap the mic for something else and see if the problem is on any connected mic.
 
Thanks for the help both of you. I tried without the cloud lifter and it's the same result. Today I'm going to hire a different sm7b to see whether it is just my new mic. Don't want to go through the returns process unless I actually know it's an issue or not. Will report back!
 
I'm going to have to reconsider this one. I'm at home but remembered there was a clip of my SM7B on the server and I grabbed it and loaded it into Audition on this MacBook Pro. There is an identical black line at the same frequency. This really surprised me - so the clip was from the comparisons I did to check polarity - so I brought in another microphone - a Beyer M58 omni. No black line! Tried the other clips and it is just the SM7B that has that 6.8K deep notch. There's a line at 10K - but it is in every clip at a very low level - so that's a computer or interface artefact. The SM7B does have the 'feature' you have noticed. Totally bizarre!
 

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This is so weird! Thanks for confirming Rob. I am doing some testing now with an sm7b that I hired and there are very similar results with this one too, though it isn't as pronounced

LEFT: Hired sm7b
RIGHT: My sm7b

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Keep doing tests and keep coming up with the same result. My sm7b on the left, the hired one on the right.

What do you think, should I just stick with the mic or may there be something wrong with it?

1643940885554.png
 
It wasn't that long ago that we didn't have the tools to know what the sound looked like. If it sounds good, it doesn't matter what the graph looks like.
 
I’ve had mine for ages and never noticed. I wonder if it’s something to do with the heavy metal grill? Some kind of resonant effect that impacts the audio passing through, like dead notes on guitars when springs or strings suck the life out of certain notes? I certainly can’t hear it but never noticed this ‘feature.
 
So I got a replacement. Result is not as pronounced as my previous mic and sounds great to my ears. I'm happy with it :D. What a strange discovery. Thanks everyone!
 
This notch just made no sense - with some research I can't find any examples of this phenomenon happening, so I did a different test.

Using the Tascam interface (one I am totally happy with), there is the notch at 6.8K.

Today, I put the SM7B in front of loudspeakers producing pink noise and recorded into the interfaces available to be here:
Tascam 1641 - a black line, not that deep but visible at 6.8K ONLY on SM7B - SM58 used as comparison, notch free.
Zoom H6 - no notch visible at all on either mic
Midas M32 - again, no notches.

The conclusion is the notch is produced in the Tascam, and further testing of the Tascam using NO microphone, but simply normalising the preamp noise reveals some quite unpleasant spikes, produced internally. Without the normalisation they are totally inaudible, but maybe there are not just spikes, but notches, and the extra gain required with the SM7B raises them above the noise floor so they can be seen, if not heard? There is no notch I can detect on the SM7B using a different preamp/interface, but it is there on the Tascam.

If anyone has time to waste, and has a DAW that can normalise - pull out your mic connector and record the silence and normalise it. If you have a spectrum scope or or other tool in a menu somewhere - I discovered Cubase's spectrum display today for the first time - this gives a simple line graph of level vs frequency and the spikes are quite pronounced. Lots of the little peaks are mathematically linked, I note - so a little peak every two KHz indicates perhaps internally generated artefacts - in the preamp, or DAW I do not know, but it is interesting.
 
I really don't know? The interface appears to be causing the notch, and in mine, a spurious peak - very low in level at 10K. Then the analysis tools in the DAW might be not so good at showing these things, and maybe the DAW is adding it's own input to the party - I really don't know, but I cannot hear them - but I can clearly see them!
 
Attached is my KA6 with the mic pre amp noise normalized to 0dBfs. Looks just random to me? Note I cannot attache the test .wav and MP3 will surely crappifier any information so contained! That is from Right Mark Analyser BTW.

Dave.
 

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rob aylestone said:
That's a lot better than I was getting. I'll try the same on my presonsus when I get a chance.
Click to expand...
It is a shame my M4 is in transit to son in France as I suspect that would be even better. I am reminded of the plots I got from people's low rent USB mixers. The 16 bit converters spiked about 6dB above the 85dBfs noise floor at 1kHz and continued every octave to 20kHz.

Dave.
 
rob aylestone said:
This notch just made no sense - with some research I can't find any examples of this phenomenon happening, so I did a different test.

Using the Tascam interface (one I am totally happy with), there is the notch at 6.8K.

Today, I put the SM7B in front of loudspeakers producing pink noise and recorded into the interfaces available to be here:
Tascam 1641 - a black line, not that deep but visible at 6.8K ONLY on SM7B - SM58 used as comparison, notch free.
Zoom H6 - no notch visible at all on either mic
Midas M32 - again, no notches.

The conclusion is the notch is produced in the Tascam, and further testing of the Tascam using NO microphone, but simply normalising the preamp noise reveals some quite unpleasant spikes, produced internally. Without the normalisation they are totally inaudible, but maybe there are not just spikes, but notches, and the extra gain required with the SM7B raises them above the noise floor so they can be seen, if not heard? There is no notch I can detect on the SM7B using a different preamp/interface, but it is there on the Tascam.

If anyone has time to waste, and has a DAW that can normalise - pull out your mic connector and record the silence and normalise it. If you have a spectrum scope or or other tool in a menu somewhere - I discovered Cubase's spectrum display today for the first time - this gives a simple line graph of level vs frequency and the spikes are quite pronounced. Lots of the little peaks are mathematically linked, I note - so a little peak every two KHz indicates perhaps internally generated artefacts - in the preamp, or DAW I do not know, but it is interesting.
Click to expand...
 
I'm setup to do some testing here myself. I have time to waste. Carpal tunnel surgery. Bored.....

What is this Cubase spectrum display? I heard of it, but not seeing it. Thought I saw something about it in C11 - which I have upgraded to,

I have only the Steinberg UR824's as interface to test. I can test with SM7b with or without Klark CM-1 line booster.
 
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