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NT-SF1

All about the tools and techniques involved in capturing sound, in the studio or on location.

Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 11:35 am

Mike Stranks wrote:Surely more than a 'toy' Hugh?

They are all toys to me... ;) People send them, I play with them, and then they take them away again...

But I saw a T-shirt once with the slogan:

"The person who dies with the most toys wins!"

I think my bank manager thinks that might apply to me... :lol:

But seriously, it was a casual turn of phrase, rather than a damning criticism. I've not tried the thing personally, and while it is remarkably inexpensive compared to the 'traditional' SoundField offerings (of which I have two) Zoom's stuff is generally of very good quality and highly cost-effective. I'm sure this will be the same.

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Re: NT-SF1

Postby Wonks » Thu Dec 06, 2018 11:36 am

Peevy wrote:Just wondering how you go about gain matching the Rode NT-SF1. I have a Zoom F8 for on location recording, so I would imagine that would work alright, but in my studio I don’t have four stepped gain or digital preamps. What would be the routine be for gain matching the capsules?

Also, how do you work out the recording angles? … or is that not relevant with a mic such as this?
You'd need to use something to feed the same signal level in to each input in turn and monitor the level in the DAW and adjust for the same gain, say a sound from a synth using a DI box to get a mic-level signal.

I'd try it at different signal levels about 5dB apart and see how close the gain matching is, and if necessary (because you can't just set the knobs to the same value), note down the different knob settings for the different make-up gain levels required and the use those that are closest to a decent signal level when using the mic array.

But you'll really need stepped-detent gain knobs, otherwise you won't be able to reproduce the matched levels accurately if they are just normal pots. So if you don't want to use the Zoom in the studio and your pre-amps just have pots, then you will be best investing in an interface that does have stepped gain knobs or the gains can be set digitally.

As I understand it, as the mic is designed to pick up 360° sound, there is no 'front' to the mic, so the angle is irrelevant.
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Re: NT-SF1

Postby ef37a » Thu Dec 06, 2018 11:37 am

Peevy wrote:Just wondering how you go about gain matching the Rode NT-SF1. I have a Zoom F8 for on location recording, so I would imagine that would work alright, but in my studio I don’t have four stepped gain or digital preamps. What would be the routine be for gain matching the capsules?

Also, how do you work out the recording angles? … or is that not relevant with a mic such as this?

I WAS going to say that the individual capsules will already be gain matched but looking at the specification it does not say so! There is the 30mV/Pa sensitivity but no tolerance.
I can only assume, like buying a matched stereo pair that they are closely matched?

As for the pre amps? I said earlier. You will have to get that old Levell sig genny out and use a fine tip Magic Marker!

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Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 11:48 am

Peevy wrote:Just wondering how you go about gain matching the Rode NT-SF1. I have a Zoom F8 for on location recording, so I would imagine that would work alright, but in my studio I don’t have four stepped gain or digital preamps. What would be the routine be for gain matching the capsules?

Yes, it is certainly an issue if you don't have preamps with a well defined gain adjustment system in place. The best I can offer is to acquire one of those plug-in XLRs that generates a mic-level test tone, and use that to align the four mic preamp channels to some suitable gain.

For example:
Image
https://www.canford.co.uk/CANFORD-PHANTONE-TONE-GENERATOR

Image
https://www.parts-express.com/gold-line-gl1k-microphone-level-input-tester--390-860

Image
https://www.shure.com/americas/products/accessories/microphones/microphone-problem-solvers/a15tg-tone-generator

The process would be to adjust the gains of the four mic preamps during a rehearsal to achieve a sensible gain structure with plenty of headroom. Obviously, the capsules closest the loudest sources will produce more level than the others... so the idea is to look at the loudest output and set all the other preamps to the same gain by eye. Then disconnect the mic and plug the test tone generator into one preamp and note the meter reading. Then plug it into each of the other preamps in turn and fine-tune their gains to achieve exactly the same meter reading. And finally, replug the mic! That way you will have perfectly aligned preamp gains in all our channels, even if the gain controls end up pointing at slightly different places!

This ain't new rocket science, either... Some of the very early Calrec SoundField mics in the 70s had a built-in test oscillator precisely for this purpose, and it would have been sensible if the Rode (and other Ambisonic) mic(s) included a test oscillator to send the a reference level to all four outputs -- precisely so that you could align the gains of a independent variable-gain preamps... but they didn't... presumably to keep the cost down.

And actually, even if they did, with electret capsules it wouldn't be guaranteed to be accurate after a few years anyway as the capsules' sensitivities will inherently decrease over time and not necessarily all at the same rate...

Also, how do you work out the recording angles? … or is that not relevant with a mic such as this?

It is relevant in so far as the decoded outputs can emulate conventional coincident mic arrays, but you have the ability to change those arrays in post-production to suit the recording requirements. So you can change the decoded virtual mic polar patterns and mutual angles, which will alter the stereo recording angles after the event...

So rather than worrying too much about the stereo recording angles, it's actually more important to make sure the placement is optimised in terms of direct/reflected sound balance (although that will also vary to a degree as the emulated coincident arrays are adjusted).

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Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 11:52 am

ef37a wrote:I WAS going to say that the individual capsules will already be gain matched but looking at the specification it does not say so!

Yes, of course they are matched in the factory. It's a critical aspect of the unit as a whole that all four outputs have equal sensitivity. Although I don't know what tolerances the different ambisonic mic makers work too... I would assume that the very expensive high-end SoundField stuff has tighter tolerances than some of the much simpler and cheaper alternatives...

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Re: NT-SF1

Postby ef37a » Thu Dec 06, 2018 1:05 pm

Hugh Robjohns wrote:
ef37a wrote:I WAS going to say that the individual capsules will already be gain matched but looking at the specification it does not say so!

Yes, of course they are matched in the factory. It's a critical aspect of the unit as a whole that all four outputs have equal sensitivity. Although I don't know what tolerances the different ambisonic mic makers work too... I would assume that the very expensive high-end SoundField stuff has tighter tolerances than some of the much simpler and cheaper alternatives...

H

Did not not know about those inline tone generators Hugh. Most handy and I would suggest anyone involved in sound recording or repro put one in their gig bag. The Shure one is a bit pricey but does at least work from my hearing aid batteries!

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Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 3:32 pm

ef37a wrote:The Shure one is a bit pricey but does at least work from my hearing aid batteries!

:bouncy: This is a bit Schrodinger's cat-like. If you put your hearing aid batteries in the tone genny, how will you know if it's generating tone? :lol:
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Re: NT-SF1

Postby Sam Spoons » Thu Dec 06, 2018 3:35 pm

Perhaps he should buy a phantom powered one, then at least his deceased relatives will be ble to tell him :D
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Re: NT-SF1

Postby Peevy » Thu Dec 06, 2018 3:50 pm

Thanks for the replies to my question and thanks Hugh for your detailed response and various gadget suggestions.

I think I’ll hold off just now on a purchase until I can rig up an easier way to gain match the four capsules in my studio to whatever the source is. I’m wondering if I would be able to use the Zoom F8 as an audio interface simultaneously with my RME Fireface 802. (I’ve never tried out the audio interface aspect of the F8)
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Re: NT-SF1

Postby ef37a » Thu Dec 06, 2018 4:58 pm

Hugh Robjohns wrote:
ef37a wrote:The Shure one is a bit pricey but does at least work from my hearing aid batteries!

:bouncy: This is a bit Schrodinger's cat-like. If you put your hearing aid batteries in the tone genny, how will you know if it's generating tone? :lol:

Cheeky sod! I am not really deaf. I am convinced people just mumble to themselves and the line level on telephones is 20dB down on what it was 20yrs ago. TV sound has a permanent LPF starting at 2kHz and dialogue is always 10dB below any incidental music or FX. Even on Radio3 the music rarely gets louder than the link person!

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Re: NT-SF1

Postby ConcertinaChap » Thu Dec 06, 2018 5:33 pm

Mike Stranks wrote:The B&H reviewer begged to differ... he said Apollo space capsule... :D

Actually I've managed to find a picture of a Mercury capsule complete with astronaut. I rest my case.

Image

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Re: NT-SF1

Postby Wonks » Thu Dec 06, 2018 5:39 pm

Astronaut? That's just a space cadet! ;)
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Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 5:51 pm

Oooh... you guys!

:D :bouncy: :lol:
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Re: NT-SF1

Postby Sam Spoons » Thu Dec 06, 2018 7:31 pm

I presume the 'exit' button is in the inside :smirk:
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Re: NT-SF1

Postby Mike Stranks » Thu Dec 06, 2018 8:15 pm

G-C:
Ground-control to Hugh Robjohns... Ground-control to Hugh Robjohns... Your circuit's dead; there's something wrong...

HR:
I think you'll find that if you reset the LUFS to -15, switch off the HPF and then normalize to -0.5dB all will be well....
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Re: NT-SF1

Postby Hugh Robjohns » Thu Dec 06, 2018 8:52 pm

:clap: :lol:
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Re: NT-SF1

Postby The Korff » Fri Dec 07, 2018 11:36 am

Morning chaps!

Just FYI, I've been in touch with Zoom about getting the H3-VR in for review. Will report back when I hear more...
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Re: NT-SF1

Postby ConcertinaChap » Fri Dec 07, 2018 12:58 pm

Excellent, thanks!

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Re: NT-SF1

Postby Mike Stranks » Fri Dec 07, 2018 2:41 pm

The Korff wrote:Morning chaps!

Just FYI, I've been in touch with Zoom about getting the H3-VR in for review. Will report back when I hear more...

Thank you young sir!

A request: Whoever reviews can they can the measurement tools out to establish things like noise-floor, freq response. end-end S/N ratio etc?

I thenk yew!
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Re: NT-SF1

Postby The Elf » Fri Dec 07, 2018 3:10 pm

...and please tell those of us who are still confused just how to use the thing! :headbang: :lol:
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