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High noise, low signal on NTG4+ - would a mixer help?

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High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 11:25 am

Hi,

I have an NTG4+ which I use either with a TD70 for camera work, or a Roland Rubix 24 interface to go into the computer. The problem I am having is I have to put the input gain almost max to get a decent signal - even if I am talking into it like an SM58... (which actually, I'm tempted to get instead - this is for podcasting use and I want that close-up sound).

Obviously, when the gain is so high, there is a lot of background noise and the mix is even picking up noises from downstairs like my wife and child laughing etc (not at me, I hope!)

Just for the record as I know this will be asked. Yes, 48V is on, no, the -10db pad isn't on ;) Rubix 24 is powered by a 5v power supply, not via USB. I do have a computer in the room, but there's not too much I can do about that at the moment, and it seems odd that I'd have to crank the input gain in the 24 more or less to max to get a decent signal in.

Would a small mixing desk with decent pre-amps fix this? I want something with a USB interface - and ideally more than 2 channels. Money is tight at the moment so I'm considering the Zedi-10 (not the FX) which has 4 in/4 out USB and I can get for 205 euros locally. Would the mic pre-amps on there be any better than the 'low-noise' pre-amps on the Rubix 24? I don't want to waste my money on the wrong solution (and really I want a desk with faders on each channel but ...)

Thanks
John
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby Hugh Robjohns » Tue Jul 07, 2020 11:58 am

From your descriptions I suspect what you are hearing is acoustic noise rather than electronic noise.

The NTG4+ has a pretty high sensitivity at 25mV/Pa, so you really shouldn't need a massive amount of preamp gain if you're using the mic up very close to your mouth.

I know you're using phantom, and I see the Rubix specs say it is 48V (not all are!) but that it is restricted to 6mA which is below the full spec level of 10mA. I doubt the NG4+ needs more than that, but some mics do... so it might be worthwhile switching phantom off and running the mic using its internal battery option just to see if it makes any difference.

I can't find any specs for the preamp EIN figure, so I don't know ho noisy it really is.
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 12:27 pm

Hugh Robjohns wrote:From your descriptions I suspect what you are hearing is acoustic noise rather than electronic noise.

The NTG4+ has a pretty high sensitivity at 25mV/Pa, so you really shouldn't need a massive amount of preamp gain if you're using the mic up very close to your mouth.

I know you're using phantom, and I see the Rubix specs say it is 48V (not all are!) but that it is restricted to 6mA which is below the full spec level of 10mA. I doubt the NG4+ needs more than that, but some mics do... so it might be worthwhile switching phantom off and running the mic using its internal battery option just to see if it makes any difference.

I can't find any specs for the preamp EIN figure, so I don't know ho noisy it really is.

Yes, I think it is acoustic noise, I've had digital noise on the rubix 24 before but using external power and the ground lift fixed that. It seems to be because I have to have the input gain SO high to get a decent level.

I didn't know that about the current restriction on the Rubix 24. I can't find the current specs on the Zedi-10 preamps. As they boast they are gs preamps, I'd like to think they'd supply 10mA but without specs, who knows.

Good idea trying it from the battery. It's on charge now (I don't normally use it charged).

I have just found a very very very old Behringer Tube Ultragain Mic100 in my drawers of crap - don't laugh - and wondering if it might be worth testing that to see if it makes any difference although I suspect it will just add more noise ;)

Thanks

ps. the RIGHT answer was 'Yes, the mixer will fix your problems, go buy it now, in fact, buy the one you really want no matter how much it costs' ... ;)
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby Sam Spoons » Tue Jul 07, 2020 12:38 pm

I'm wondering how the mic can be picking up excessive noise from people downstairs when you are using it close up (with an SM58 1-2" from your lips is it's natural habitat but you would not want to be quite that close with the Rode)? If you speak at normal levels the wanted audio (i.e. your voice) should be a lot louder than the background. Do you have a recording you could post to illustrate the problem you are having?
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 12:39 pm

Actually, just read the NTG4+ specs and it only needs 4.8 mA so unlikely to be that. I'll still try of course.

Thanks
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby Hugh Robjohns » Tue Jul 07, 2020 1:43 pm

johnr10 wrote:Actually, just read the NTG4+ specs and it only needs 4.8 mA so unlikely to be that.

Didn't expect it was the problem, but you have to rule things out.... Another possibility is that the 48V phantom isn't actually 48V. That happens surprisingly often. Again, running on internal battery will rule that possibility out too...

With a mic having a 25mV/Pa sensitivity and located only a few inches from the mouth, with normal speech you really shouldn't need more than about 40dB of gain. Having to run the preamp flat out doesn't sound right at all.

Have you checked with a different XLR cable in case the original cable is one-legged (one of the signal wires broken)?
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 4:05 pm

Hugh Robjohns wrote:
johnr10 wrote:Actually, just read the NTG4+ specs and it only needs 4.8 mA so unlikely to be that.

Didn't expect it was the problem, but you have to rule things out.... Another possibility is that the 48V phantom isn't actually 48V. That happens surprisingly often. Again, running on internal battery will rule that possibility out too...

With a mic having a 25mV/Pa sensitivity and located only a few inches from the mouth, with normal speech you really shouldn't need more than about 40dB of gain. Having to run the preamp flat out doesn't sound right at all.

Have you checked with a different XLR cable in case the original cable is one-legged (one of the signal wires broken)?

I've tried two cables, and also tested them with a multimeter and they are fine.

Running with the battery has made no real difference. There's possibly a bit of electrical hum with the '48v' from the Rubix, which is measuring at 44.3v
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 4:06 pm

Sam Spoons wrote:I'm wondering how the mic can be picking up excessive noise from people downstairs when you are using it close up (with an SM58 1-2" from your lips is it's natural habitat but you would not want to be quite that close with the Rode)? If you speak at normal levels the wanted audio (i.e. your voice) should be a lot louder than the background. Do you have a recording you could post to illustrate the problem you are having?

I've just made some test recordings. I have to rush out to view a house. Can I message you with a link to them when I get back, rather than post them? Thanks
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby Sam Spoons » Tue Jul 07, 2020 4:36 pm

Better to post them so the 'hive mind' can get to work on the problem :thumbup:
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 7:14 pm

Sam Spoons wrote:Better to post them so the 'hive mind' can get to work on the problem :thumbup:

Fair enough!

Ok, so I'm recording this on the ngt4+, connected to a Rubix 24. That is connected to the computer via USB. There are no options on the computer to change any settings for the input or output of the Rubix.

It's going in to Logic Pro X, recorded on a new audio track, no settings changed except to change the track input from 1&2 to only 1.

First file - https://workdrive.zohopublic.eu/externa ... F4l-lU5Xxz

It starts very quietly (on 50% input gain). Mic is powered by the '48v' from the Rubix, and I'm using this XLR cable - https://www.amazon.co.uk/dp/B016D50A1Y/ ... UTF8&psc=1

The waveform is basically flat at 50% input gain, and ok at 100% - with the obvious issues that brings.

I mentioned before I had tested it with two cables, but they are both the same brand - bought a year apart. Both are 3m (which is longer than I need but not too long to cause this problem!)

The mic is on a cheap Neweer arm which is attached to a shelf on the (solid) wall, isolated from my desk. The mic is sitting in a Rode SM3-R shock mount (https://www.amazon.co.uk/R%C3%98DE-SM3- ... 01LVZUCJM/)

The second file - https://workdrive.zohopublic.eu/externa ... F4k-lU5Xxz

In this file I say the door is closed, it wasn't. It was open, sorry. This file also tests it with 48v from the Rubix and then the internal battery of the mic.

Really hoping I am doing something very stupid (or that I can use this as a good excuse to buy a mixer ;) )

Thanks in advance. Be warned, again, they start low at 50% gain, but do go loud when I go to 100% gain so be prepared for it to go loud and for noise.

Thanks
John
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby James Perrett » Tue Jul 07, 2020 9:28 pm

The first file makes me think that most of your noise is acoustic. Our ears are very good at ignoring background noise but, when listening to a recording, the noise becomes much more apparent.

The noise on the very last segment (on battery power) sounds different and much more like preamp noise. Was the vacuum cleaner running at the time?

Do you have a dynamic mic that you can try at the same settings to see if the noise level is the same?
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 9:36 pm

James Perrett wrote:The first file makes me think that most of your noise is acoustic. Our ears are very good at ignoring background noise but, when listening to a recording, the noise becomes much more apparent.

The noise on the very last segment (on battery power) sounds different and much more like preamp noise. Was the vacuum cleaner running at the time?

Do you have a dynamic mic that you can try at the same settings to see if the noise level is the same?

No, unless I have something really crap somewhere from years ago, I don't think I have another mic. I was considering getting an SM58 which I guess would do the job of testing it, but if I then have to spend more money on a mixer with better pre-amps because it's something else...

I'm sorry, I can't remember if the vac was running then. Very possibly. But it's a silly robot thing and I didn't turn it on and it has a mind of its own when it decides to stop and start sometimes ;) But even if it was, it was downstairs.

But what really concerns me is the levels. Having to have the gain so high to register a strong signal that I can hear things in other rooms for a condenser seems wrong (I'm fair from an expert as I'm sure is apparent), but the ntg4+ shouldn't pick up much from behind, and the gain is so loud that when i lightly touched soft tissue behind the mic, it was crystal clear?!

Thanks
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby Sam Spoons » Tue Jul 07, 2020 10:23 pm

As far as I can tell you issue is simply the ratio of background noise to wanted audio. The second clip reveals what appears to be preamp noise (unless, as James suggests the vacuum cleaner was running in the room) so that discounts the battery option as a cure.

The only way to improve things is to get more voice or less background (or both) into the mic. So to improve the first, get closer to the mic and speak louder, to reduce the second, close the door, make door seals so the door doesn't leak noise and/or record only when your wife and kids are not in the house.

I'd be inclined to do both, make sure external sound leaking into you room is minimised by sealing the doo and ensuring it is closed when recording and get closer to the mic. Then think about some acoustic treatment around your recording position, a close mic will help and your test recordings are not too bad but a couple of duvets hung around you when you record will help absorb any reflections off the walls (duvets are tricky to set up to remove ceiling reflections but it's just a matter of achieving the best compromise you can.

johnr10 wrote:But what really concerns me is the levels. Having to have the gain so high to register a strong signal that I can hear things in other rooms for a condenser seems wrong (I'm fair from an expert as I'm sure is apparent), but the ntg4+ shouldn't pick up much from behind, and the gain is so loud that when i lightly touched soft tissue behind the mic, it was crystal clear?!

See above, it's not the high gain that's the problem it's the fact that you voice is generating -35dB (at your 50% gain setting) and the background noise is at -72, when you turn the gain up to 100% the voice is generating -3dB and the background -27dB. Turning the gain up or down will turn the voice and the background equally.

Finally, to add if you double the distance between the source and the mic you will see a 6dB decrease in level so going from 2" away to 8" away will decrease the voice level by 12dB, when you then turn up the gain to get a similar level into the recorder the background noise (which hasn't got further from the mic) also comes up by 12dB.
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 10:42 pm

Sam Spoons wrote:As far as I can tell you issue is simply the ratio of background noise to wanted audio. The second clip reveals what appears to be preamp noise (unless, as James suggests the vacuum cleaner was running in the room) so that discounts the battery option as a cure.

The only way to improve things is to get more voice or less background (or both) into the mic. So to improve the first, get closer to the mic and speak louder, to reduce the second, close the door, make door seals so the door doesn't leak noise and/or record only when your wife and kids are not in the house.

I'd be inclined to do both, make sure external sound leaking into you room is minimised by sealing the doo and ensuring it is closed when recording and get closer to the mic. Then think about some acoustic treatment around your recording position, a close mic will help and your test recordings are not too bad but a couple of duvets hung around you when you record will help absorb any reflections off the walls (duvets are tricky to set up to remove ceiling reflections but it's just a matter of achieving the best compromise you can.

Thanks. I do already have some acoustic treatment in the room (the difference between when it was bare and now is *stark*). I also have two thick panels to cover two lwindows but they are not hanging up at the moment but they make a big difference too.

The vac was downstairs, not in the room btw.

I wouldn't normally record with the door open, but what concerns me is the signal is so low. It needs to be at 100% gain to get a decent waveform. At 50% it's basically flat, at 75%, it's still low. And it's at 75% the noise really starts showing. Yes, I could go closer - and I have done during some of this testing in the last few days - but it's still noisy. Maybe I'm just being overly fussy?

I've had this mic about 18 months or so, done quite a few videos with it - with the mic at least 12 inches away, and not really had a problem so I'm really confused as to what is going on now (although in the past I have recorded the audio on my 70D, not straight into the computer via the Rubix)). Perhaps the noise has always been there but I've just not noticed, although that seems hard to believe.

Now I'm going more for a podcasting setup (with video, but I want the audio to be more 'radio like' rather than just clean). I did try it in to the 70D and back out to the Rubix at the weekend, but no matter what I tried I couldn't get an acceptable signal and as this is for podcasting rather than making videos, I need it to go into the computer live, not onto the sd card.

Perhaps I'm best getting a dynamic mic instead (well, not instead, I'll keep the ntg4+ for other uses of course).

I'd get the SM7B if I could afford it but I can't justify it at the moment. The SM58 would be fine probably but it simply looks crap - and this is video too, so sadly that is a factor. Maybe something like a Podmic or an AT2020 xlr?

Thank you for your time (everyone), it really is appreciated.
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Re: High noise, low signal on NTG4+ - would a mixer help?

Postby johnr10 » Tue Jul 07, 2020 10:48 pm

johnr10 wrote:But what really concerns me is the levels. Having to have the gain so high to register a strong signal that I can hear things in other rooms for a condenser seems wrong (I'm fair from an expert as I'm sure is apparent), but the ntg4+ shouldn't pick up much from behind, and the gain is so loud that when i lightly touched soft tissue behind the mic, it was crystal clear?!

See above, it's not the high gain that's the problem it's the fact that you voice is generating -35dB (at your 50% gain setting) and the background noise is at -72, when you turn the gain up to 100% the voice is generating -3dB and the background -27dB. Turning the gain up or down will turn the voice and the background equally.

Finally, to add if you double the distance between the source and the mic you will see a 6dB decrease in level so going from 2" away to 8" away will decrease the voice level by 12dB, when you then turn up the gain to get a similar level into the recorder the background noise (which hasn't got further from the mic) also comes up by 12dB.[/quote]

Ah, did you add this after you posted and as I was replying?

Yes, I'm aware the background noise will rise with the signal, I just don't understand why there is so much background noise, and why the signal is so weak in the first place?

As I said in my last reply, i've done a lot of videos with this mic at 12 inches or so away, and never noticed a problem before. It's just I want that close 'radio' sound now and trying to get that has brought up these problems. When I recorded in the past on the 70D (sorry, I have a feeling I typed DR70 or something before?!) and imported from the sd card, I never noticed a weak waveform or lots of noise..?!
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