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Gain staging RE20/SM7B through ISA 428 & RODEcaster
Old 2nd December 2019
  #1
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Gain staging RE20/SM7B through ISA 428 & RODEcaster

Hello (first post, welcoming feedback on format etc.),

I'm getting some noise from SM7B and RE20 which are in a vocal booth. Using studio to record podcast style content. I'll need at least 60 gain, and that's when noise starts showing up. Even when using gating the noise is audible in voice tracks.

Cybepower CPS-1215RM is power source.

Setup uses all XLR-XLR Mogami gold cables (longest is 12 ft from mics to pre).

For each mic, the chain is Mic->ISA 428 Mkii->Behringer Multicom Pro-XL>-RODECaster Pro. RODEcaster uses usb interface with workstation. Interface levels turned all the way down.

I'm suspecting the noise is coming from the RODECaster as there is no direct line in (currently running xlr from compressor into RODEcaster), which is presumably going through the pre-amp in there. Curious if there are other steps I could take to gain stage or problem solve.
Old 3rd December 2019
  #2
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scrubs's Avatar
 

In general, try to have as much gain a you can closest to the mic. Looks like the ISA alone can put out ~80dB of gain (+60 input, +20 output trim), which should be more than enough. I'd start with the output trim on the ISA all the way up, then increase the input gain to get a healthy signal.

Do you even need the Rode in your setup? If so, you shouldn't need to add more gain with it - just set it at unity.
Old 3rd December 2019
  #3
Gear Head
Not saying it’s the case here, but in my roundabout journeys through noise reduction, the #1 issue I’ve identified is multi-faceted signal paths irrespective of cable lengths/models. Every in/out jack is a 2-point connection from one’s output to another’s input, where there could be a lose solder point, poor resting position, cable strain, etc... not to mention the varying inconsistent, shoddy/aging electronics and circuits... so I streamline where possible.

I’d go straight from preamp output to line-input of your chosen converter/interface and deal with all dynamics ITB. Based solely on i) a 4-point signal flow and ii) you’re reporting noise issues with a preamp where there should be none, that’s the first step I would take, no question. Multi-faceted signal flows to my experience are always way cooler in theory than practice.

Putting all that aside, I’ve always avoided Behringer in any recording path.
Old 3rd December 2019
  #4
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Quote:
Originally Posted by scrubs View Post
In general, try to have as much gain a you can closest to the mic. Looks like the ISA alone can put out ~80dB of gain (+60 input, +20 output trim), which should be more than enough. I'd start with the output trim on the ISA all the way up, then increase the input gain to get a healthy signal.

Do you even need the Rode in your setup? If so, you shouldn't need to add more gain with it - just set it at unity.
I can get the gain high enough, but when monitoring (in the sound proof vocal booth) there is still a light hum of noise at -54db or so. It's not the Behringer, as I ran direct from pre to RODEcaster and still same hum. I'm just struggling with how much hum is normal at -50db when gain is at 60-65 on 428. makes me wonder if it is in fact the RODE adding the noise, but would need another interface to test.
Old 4th December 2019
  #5
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Quote:
Originally Posted by justmusic View Post
Not saying it’s the case here, but in my roundabout journeys through noise reduction, the #1 issue I’ve identified is multi-faceted signal paths irrespective of cable lengths/models. Every in/out jack is a 2-point connection from one’s output to another’s input, where there could be a lose solder point, poor resting position, cable strain, etc... not to mention the varying inconsistent, shoddy/aging electronics and circuits... so I streamline where possible.

I’d go straight from preamp output to line-input of your chosen converter/interface and deal with all dynamics ITB. Based solely on i) a 4-point signal flow and ii) you’re reporting noise issues with a preamp where there should be none, that’s the first step I would take, no question. Multi-faceted signal flows to my experience are always way cooler in theory than practice.

Putting all that aside, I’ve always avoided Behringer in any recording path.


Having a hard time with this one. I am putting 65db gain from 428 and still getting a low hum (from a sound proof vocal booth) at around -57 on the monitor. My vocal tracks are hitting somewhere in the -16to -12 zone. Without gate, the hum is audible on track. Less audible when gated. I've bypassed the 4600 and hum still present. Made some progress today by reducing the gain but increasing the impedance. And, by reducing DB on the back of the 4600. I am also wondering if this could perhaps be some type of grounding issue, the building that the studio is in is old.
Old 4th December 2019
  #6
Gear Head
Have you tried printing a lower level file and using a gain plugin with +10dB or more?

Could also try removing the rackmount power source and using a smaller/household outlet box instead. Just to identify if the rack’s the issue...

Or tear down and reset in a different building to find out if it’s a grounding issue.
Old 6th December 2019
  #7
Gear Nut
 

Quote:
Originally Posted by justmusic View Post
Have you tried printing a lower level file and using a gain plugin with +10dB or more?

Could also try removing the rackmount power source and using a smaller/household outlet box instead. Just to identify if the rack’s the issue...

Or tear down and reset in a different building to find out if it’s a grounding issue.
He's using a mic pre (ISA428) with 80dB of gain (!)..he should not need a gain plugin that adds noise to the noise.
It's a hardware problem (gain staging issue between ISA and Rodecaster) he should find a hardware solution.

Last edited by johnjj; 12th December 2019 at 03:37 PM..
Old 6th December 2019
  #8
Gear Nut
 

Quote:
Originally Posted by scrubs View Post
In general, try to have as much gain a you can closest to the mic. Looks like the ISA alone can put out ~80dB of gain (+60 input, +20 output trim), which should be more than enough. I'd start with the output trim on the ISA all the way up, then increase the input gain to get a healthy signal.

Do you even need the Rode in your setup? If so, you shouldn't need to add more gain with it - just set it at unity.
This is the way to go :
On the ISA 428 : output trim all the way up, then gradually adjust the gain (still on the ISA)
On the Rodecaster : Line inputs, if no line inputs use mic inputs with gain at zero/unity

It's not clear if the Rodecaster pro has dedicated line inputs (i.e bypassing rodecaster preamp stage)
If it doesn't have dedicated line inputs, set the mic input gain on the Rodecaster at zero/unity..maybe that will bypass rodecaster's preamp.
Report how it fares that way :-)

Make sure no effects (aural exciter...bottom) are engaged : these can induce a lot of noise.
Make sure the noise doesn't come from other channels
Old 6th December 2019
  #9
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Quote:
Originally Posted by johnjj View Post
This is the way to go :
On the ISA 428 : output trim all the way up, then gradually adjust the gain (still on the ISA)
On the Rodecaster : Line inputs, if no line inputs use mic inputs with gain at zero/unity

It's not clear if the Rodecaster pro has dedicated line inputs (i.e bypassing rodecaster preamp stage)
If it doesn't have dedicated line inputs, set the mic input gain on the Rodecaster at zero/unity..maybe that will bypass rodecaster's preamp.
Report how it fares that way :-)
I'll have to try this on Monday. I went ahead and purchased another interface and some TRS lines to go from ISA to interface. Although it theoretically shouldn't matter, I'm suspecting the pre on the rodecaster is adding noise, even with gain level all the way down. I've turned off all effects on the rodecaster and am running it multitrack to daw (bypassing level control).

As to 428 suggestion, isa428 operates at a constant output level, so gain is the only controllable variable for increasing volume.

Also going to test building grounding and try to eliminate any potential ground loops. Suggestions or links for this would be helpful.
Old 9th December 2019
  #10
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Here's an update. I switched to another interface and ran line outputs from compressor. It's better, but still getting some noise. Here is an interesting observation:

When the gate is on compressor, and closed (theoretically no noise should come through), the noise becomes louder when I crank gain on preamp.

As a reminder, pre->compressor->interface. The pre and compressor are all in the same rack (gator portable rack) pre on top of compressor. Wondering if hum is some type of electrical interference from these two being close. Have ordered some hum x plugs to see if they help.

Thoughts?

Also quick Q ffor those using Shure sm7b and re20, what's a reasonable noise floor in a recording booth? -72? -85?


Also the noise is not exactly stable, it bounces a bit. 2-4db.
Old 10th December 2019
  #11
Gear Head
Quote:
Originally Posted by srsly_sam View Post
Here's an update. I switched to another interface and ran line outputs from compressor. It's better, but still getting some noise. Here is an interesting observation:

When the gate is on compressor, and closed (theoretically no noise should come through), the noise becomes louder when I crank gain on preamp.

As a reminder, pre->compressor->interface. The pre and compressor are all in the same rack (gator portable rack) pre on top of compressor. Wondering if hum is some type of electrical interference from these two being close. Have ordered some hum x plugs to see if they help.

Thoughts?

Also quick Q ffor those using Shure sm7b and re20, what's a reasonable noise floor in a recording booth? 72? 85?


Also the noise is not exactly stable, it bounces a bit. 2-4db.
Ditch the Behringer. Any improvement?
Old 10th December 2019
  #12
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Quote:
Originally Posted by justmusic View Post
Ditch the Behringer. Any improvement?
Still there, it looks like it's coming from the 428.
Old 11th December 2019
  #13
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Quote:
Originally Posted by srsly_sam View Post
Still there, it looks like it's coming from the 428.
Here is a .wav with a sample of the noise floor. This is not normalized, compressed, or expanded.
Attached Files

noise floor.wav (3.20 MB, 283 views)

Old 12th December 2019
  #14
Gear Nut
 

Quote:
Originally Posted by srsly_sam View Post
As to 428 suggestion, isa428 operates at a constant output level, so gain is the only controllable variable for increasing volume.
Ah... I forgot about that, it's the other way around...I haven't used an ISA preamp for a long time, I remember liking them though.
Is that audio clip done with the mic plugged through ISA and then ISA out directly to your "new" interface?

I assume you've tried all four channels on ISA428....

Did you try (like justmusic suggested)
- removing the rack power source
- a different building?

If you get the same problem somewhere else and with a different power rack/power outlet,
then you might need to have your ISA checked.

Last edited by johnjj; 12th December 2019 at 04:13 PM..
Old 13th December 2019
  #15
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Quote:
Originally Posted by johnjj View Post
Is that audio clip done with the mic plugged through ISA and then ISA out directly to your "new" interface?

I assume you've tried all four channels on ISA428....
Re: Clip, yes plugged through ISA and out directly to new interface.

Here is another two clips with mic check.

It's not absolutely terrible, but it doesn't sound as good as it should. An expander helps (not on in the clips).

I plan to switch buildings late next week and see. Focusrite gave me instructions to reset the isa 428, which I didn't know was a thing. I'll also try that and report back.
Attached Files

re 20 check.wav (1.49 MB, 224 views)

sm7b check.wav (1.99 MB, 233 views)

Old 13th December 2019
  #16
Gear Nut
 

Quote:
Originally Posted by srsly_sam View Post
Re: Clip, yes plugged through ISA and out directly to new interface.

Here is another two clips with mic check.

It's not absolutely terrible, but it doesn't sound as good as it should. An expander helps (not on in the clips).

I plan to switch buildings late next week and see. Focusrite gave me instructions to reset the isa 428, which I didn't know was a thing. I'll also try that and report back.
Not too bad but yes, still hear the hiss/hum.
I hear it more on the SM7 sample as it's louder
Are you sure it's not ambient noise from the room..computer fan or anything else?
I only have my laptop at the moment, no speakers/headphones so it's hard to hear well

Whatever it is, trying again in another building will tell you what causes this.
Good luck

Last edited by johnjj; 14th December 2019 at 12:44 PM..
Old 14th December 2019
  #17
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Yes, this is in a practically noise proofed vocal booth. So it is clearly EMI or some other pre-amp/grounding problem. It is not ambient. I understand there is a noise floor for everything but this seems a bit high. Focusrite seems to think so too.
Old 20th December 2019
  #18
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So I think I may have dialed it in the best I'm going to get, and I'm reasonably satisfied with the noise level. I've attached a channel test below. I ended up having to use an expander (MDX4600), as floor still in low 60s or 70s without. Noise is barely audible in recording and tone sounds great with the re20. Gain ended up being set at approximately 63db, with level knobs on the focusrite 18iB at about 8 O'clock (6 O'clock being no level adjustment). Curious what others think.
Attached Files

re20ch1.wav (3.10 MB, 111 views)

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