Amplitude 'valleys' at around 6k and 7k

jeffagwm wrote on 5/14/2020, 8:45 PM

Does anyone have any idea what may be causing the 'valleys' in amplitude at around 6k and 7k as shown in this screen shot from Spectralayers. I am recording with a Shure SM7B into a Cloudlifter CL1 and then into a Focusrite Scarlett Solo (3rd Gen) and then directly into Vegas Pro 17. I am not applying any processing, the screenshot shows the wave form as it is recorded by Vegas. I was thinking that maybe some sort of phase cancellation caused by reflections from my computer monitors, but it doesn't change if I move the angle and placement of the mic in relation to the monitors. Would appreciate any input anyone might have. Thanks

Comments

Musicvid wrote on 5/14/2020, 9:00 PM

Got a file to go with that picture?

Tried bypassing your "Cloudlifter" DI box?

 

Dexcon wrote on 5/15/2020, 5:45 AM

I second @Musicvid 's question about whether or not you have tried leaving the Cloudlifter out of the chain. The more gadgets that are put in the recording chain, the more likely it is that some unwanted artifact/change might occur.

The SM7B is a terrific mic - does it really need additional processing in the chain? I've never used the Cloudlifter, but it seems that its purpose is to reduce feedback - so it is 'processing' the audio from the SM7B in one way or another. If feedback is a problem, it could be that you might be using speakers as a monitor while recording (that could cause feedback). If so, perhaps use headphones instead as headphones shouldn't cause feedback.

In my case, I use a condenser AKG C214 mic straight into an M-Audio M-Track Mk2 with 48V power on (because the mic is a condenser mic - not needed though for a dynamic mic like the SM7B), then USB to my computer and into Sound Forge 13. Personally, I don't 'monitor' while recording VO because it is too distracting for me.

BTW, I put one of my recent VO recordings into SpectraLayers and there were no valleys as you are experiencing.

Musicvid wrote on 5/15/2020, 8:31 AM

I would only put an active DI in the path if I was running in excess of 50 ft. of XLR or have audible hum needing a ground lift.

Even then, an SM58 still has plenty of gain. Best to look at SNR when making that sort of decision, and not pay so much attention to flat spots in the spectrum.I would be more concerned with the extra "fatness" at ~14 K, which may actually be harmonic distortion from guess what? -- the active DI. Once again, can we see a file?

Thoughts, @rraud

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Dexcon wrote on 5/15/2020, 9:16 AM

@Musicvid … yes, assuming that a USB mic (like Rode USBs) is being used. But an SM7B - or in my case an AKG C214 - are not USB. If a digital interface (DI) is not used, I am not sure how to get the recording into the computer without otherwise having to go through an analogue audio recorder (Nagra/Revox/etc perhaps) and then convert the recording to digital via import to the computer. Either way, it will still end up as a digital file.

I don't think that Cloudlifter is an amplifier for XLR purposes - it is a feedback reducer and, to my mind, is an unnecessary inclusion between an XLR connected mic and the computer. The minimum tech needed in-between an XLR cabled mic and the computer surely has to be a DI. Until computers inbuild an XLR connection (i.e. the computer will do the DI conversion - and I think that I'd prefer that specialised 3rd party products do that), what are the other options to convert analogue to digital?

Musicvid wrote on 5/15/2020, 9:35 AM

If his only preamp input connector is USB, I see the point. (Silly me, I've never owned an audio interface that doesn't have XLR.)

I don't think that box is a feedback reducer, but if it is, it works by notching frequencies. Looks like a phantom powered direct box to me, which also alters waveforms and raises the noise floor.

rraud wrote on 5/15/2020, 10:19 AM

The Cloudlifter CL1 is not a feedback control device. The CL1 was primarily designed for boosting the level of low sensitivity mics. .. ribbons for instance.

adis-a3097 wrote on 5/15/2020, 11:02 AM

Are you using a mp3 material? Or some other lossylly prerecorded programe, which you are trying to put VO on? Was the AIR mode on, as I see loots of hi-frq. content, well above 20K? Hmm...

jeffagwm wrote on 5/15/2020, 12:07 PM

As @rraud mentioned the Cloudlifter CL1 is a fixed +25dB pre-amp. The SM7B mic I am using has a fairly low output signal and needs the additional boost. Without it, I have to run the Focusrite interface at nearly full gain which produces too much self noise. There is nothing else in the signal chain. It is simply the SM7B mic, into the Cloudlifter which provides a +25dB boost to the signal, and then into the Focusrite Scarlett. I have attached another screen shot of a file that was recorded yesterday. The file is a raw file as recorded other than it has been normalized to -3dB. It has not been processed or edited other than converted to mp3 since this forum would not allow me to upload a .wav file. The screenshot clearly shows the dips in amplitude at about 6k and 7k. They are very narrow as if there is a very narrow filter being applied. I did try taking out the Cloudlifter from the signal as @musicvid suggested. It obviously made a huge difference to the signal level coming in, but did not make any difference to the amplitude dips. I did also try using an Apogee MiC+ USB mic. It did not have the dips, but while it is a good travel mic to take so we can still do auditions while on the road, it is not something I would want to actually record a project with. Plus it didn't help narrow down my trouble shooting in that it replaced everything in my signal path: Mic, Preamp and Interface. I don't currently have a second interface or a second mic to swap out to try an identify which component is affecting the signal. I have attached both another Spectralayers screenshot of the .wav file as well as a .mp3 version of the .wav file shown in the screenshot..

jeffagwm wrote on 5/15/2020, 12:22 PM

Are you using a mp3 material? Or some other lossylly prerecorded programe, which you are trying to put VO on? Was the AIR mode on, as I see loots of hi-frq. content, well above 20K? Hmm...

@adis-a3097 no, AIR Mode is not on in the signal chain. I am not using anything that will (or at least should not) be coloring the signal. As stated in my earlier post, I record .wav and deliver finished product according to clients submission criteria which may be .wav or .mp3. And again the file has not yet been processed with regards to NR, EQ, Compression, etc. This is just a raw file that I am showing to try to see if anyone has any idea what may be the cause of the amplitude dips that show up on Spectralayers at around 6k and 7k. It is on every file we record. At first I thought it may be some sort of phase cancellation caused by reflections from the monitor screens. We have 2 large screens, one for Vegas and one for scripts etc. The Script monitor is mounted above the DAW monitor so that it is line of sight when recording since we prefer to stand to read a script. However moving the mic around and even standing with my back to the monitors made no difference to the dips and so it must be something in the signal chain and since the dips are still there after removing the Cloudlifter CL1, it can only be either the Focusright Scarlet interface or the Shure SM7B mic itself.

rraud wrote on 5/15/2020, 1:11 PM

Are the mic cables decent? A compromised or low grade cable can affect the sound. I am partial to the Canare star-quad cable, but even a good quality two-conductor mic cable is usually adequate up to 100 feet (@ mic level) in a normal low RF environment. Inadequate and dirty power (voltage and amperage) is another factor to consider.

jeffagwm wrote on 5/15/2020, 1:48 PM

Are the mic cables decent? A compromised or low grade cable can affect the sound. I am partial to the Canare star-quad cable, but even a good quality two-conductor mic cable is usually adequate up to 100 feet (@ mic level) in a normal low RF environment. Inadequate and dirty power (voltage and amperage) is another factor to consider.

The mic cables are 6ft LyxPro I purchased them off Amazon last year when we set up our home studio (I have worked in the Audio/Video Production world for 30+ years but this is my first home studio that we set up for my wife's VO business.) The cables appear to be in good condition and test correctly, but that certainly could be a potential cause, if there is some sort of internal fault with one of the cables. I will try swapping the cables out to see if it makes a difference.

adis-a3097 wrote on 5/15/2020, 1:49 PM

Are you using a mp3 material? Or some other lossylly prerecorded programe, which you are trying to put VO on? Was the AIR mode on, as I see loots of hi-frq. content, well above 20K? Hmm...

@adis-a3097 no, AIR Mode is not on in the signal chain. I am not using anything that will (or at least should not) be coloring the signal. As stated in my earlier post, I record .wav and deliver finished product according to clients submission criteria which may be .wav or .mp3. And again the file has not yet been processed with regards to NR, EQ, Compression, etc. This is just a raw file that I am showing to try to see if anyone has any idea what may be the cause of the amplitude dips that show up on Spectralayers at around 6k and 7k. It is on every file we record. At first I thought it may be some sort of phase cancellation caused by reflections from the monitor screens. We have 2 large screens, one for Vegas and one for scripts etc. The Script monitor is mounted above the DAW monitor so that it is line of sight when recording since we prefer to stand to read a script. However moving the mic around and even standing with my back to the monitors made no difference to the dips and so it must be something in the signal chain and since the dips are still there after removing the Cloudlifter CL1, it can only be either the Focusright Scarlet interface or the Shure SM7B mic itself.

I see.

Well, I don't hear any "comb-filtering" in that sample of yours, so I suggest you don't show to your client that screen shot you showed us. What you cloud do is run pink noise signal through your TRS connections, as a loop, then record it and see how it behaves, if it shows the same dips in spectrum or not. If it does, contact your dealer which you bought that interface from, and you can use the screen shot of that as proof. Maybe it's just a bad unit...don't know what else to say. :)

Edit:

Plus, what rraud said!

Dexcon wrote on 5/15/2020, 7:00 PM

@Musicvid

If his only preamp input connector is USB, I see the point. (Silly me, I've never owned an audio interface that doesn't have XLR.)

I was perhaps a bit unclear here. If using a USB mic, it would be connected directly into a USB plug on the computer - there would be no need for an audio interface.

I don't think that box is a feedback reducer, but if it is, it works by notching frequencies. Looks like a phantom powered direct box to me, which also alters waveforms and raises the noise floor.

You are quite right. Goodness knows what web page I ended up on when looking for info about the Cloudlifter CL1 which is as you pointed out, and rraud further explained, a 25db signal booster.

 

Musicvid wrote on 5/15/2020, 7:23 PM

His SM7B is a higher-end dynamic vocal mic with XLR connector.

Unless the DI is needed for conversion for unbalanced preamp inputs, the mic has plenty of gain to overcome long ballanced cable runs. And the box should be attached at the preamp end, not the Mic end.

Dexcon wrote on 5/15/2020, 7:30 PM

His SM7B is a higher-end dynamic vocal mic with XLR connector.

Yes, absolutely. No question about that at all. The SM7B is a wonderful mic.

jeffagwm wrote on 5/15/2020, 9:43 PM

Just to clarify the equipment in the signal chain. The mic is a Shure SM7B which is a dynamic mic and, along with the Electrovoice RE20, is a standard in many radio stations and production houses as a vocal mic. In fact, I do believe Michael Jackson recorded Thriller on an SM7B.

Next after the mic is the Cloudlifter which provides a clean +25dB boost to the signal. The SM7B is a great mic but has a notoriously low output. In-line preamps such as the Cloudlifter are commonly used along with the SM7B to bring the output gain to a more usable level away from the noise floor.

Next after the Cloudlifter is the Focusright Scarlett digital Interface which has a USB3 connection into the computer and then into Vegas 17. All connections are with balanced XLR cables (except the Focusright to Computer which is USB3).

My question is whether anyone has ever experienced a similar effect or has a suggestion as to which of these three normally excellent items of equipment may be producing the amplitude notches in my signal at 6k and 7k? @rraud did have a good suggestion in that there may be an issue with one of the xlr cables. That idea has potential and I will get another cable and swap them out one at a time to see if it makes any difference.

Musicvid wrote on 5/16/2020, 12:31 AM

Your sample, now that you've posted it sounds wonderful. Quite honestly, sir, I suggest you stick with that, as you will not be delivering a spectrum analysis print to your audience.