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How to understand a VU Meter correctly?

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How to understand a VU Meter correctly?

Postby NT » Sat Oct 15, 2011 4:45 pm

Hi, i have recently invested into the range of uad 2 plug-ins, but am afraid i am not sure on how to read the VU meters correctly. Am fine with the likes of the VU meter showing gain reduction on a compressor, but when it comes to the output reading like ie, +4 db or +10 db on the same compressor am not sure for what i am aiming for output wise? Any help on this would be great.

Thanks,

Nick.
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Re: How to understand a VU Meter correctly?

Postby Hugh Robjohns » Sat Oct 15, 2011 5:23 pm

The zero mark on a VU meter in the analogue world is the nominal operating level (+4dBu, generally), and in the digital world I would expect it to be about -20dBFS.

The idea is to have your average level hovering around or slightly above 0VU.

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Re: How to understand a VU Meter correctly?

Postby NT » Sat Oct 15, 2011 6:39 pm

Thanks for your quick responce Hugh, think i need to catch up on my dBu's and my dBFS's,am more from a producing background rather than an engienering one i'm afraid. Ok so my aim is to have the average level around or slightly above 0VU, so i take it that going into the red is ok as long as the average level is around 0VU. Think i rememeber reading that VU meters didn't respond to high transients very well, hence going into the red, so that would make sence.

Thanks Hugh.
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Re: How to understand a VU Meter correctly?

Postby Hugh Robjohns » Sun Oct 16, 2011 12:58 pm

The VU meter (and the PPM) are analogue tools designed for the analogue world. The indicate signal levels around the nominal operating level and they don't showe the headroom margin at all.

0VU is the nominal operating level, and int he analogue world that is usually (but not always) +4dBu. Most decent analogue equipment clips at about +24dBu. This means that when signals are averaging around the 0VU point there is about 20dB of headroom to capture the fast transient peaks that the meter can't show.

Digital peak meters, in contrast do show (most) transient peaks and do show the headroom margin. The clipping point is always at 0dBFS, adn so if you build in the same kind of headroom margin in a digital system as we've always enjoyed in the analogue world, then you need to average the signal level at around -20dBFS -- at least while recording (tracking) and mixing, with transient peaks kicking up to about -6dBFS occasionally.

It has become standard practice to remove the headroom margin when it is no longer required, after final post-production and mastering of the final mix, which is why commercial music averages about -12dBFs or so and peaks to 0dBFS.

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Re: How to understand a VU Meter correctly?

Postby Martin Walker » Mon Oct 17, 2011 4:18 pm

Just to add my two 'pennorth - I've found -18dBFS is a more common reference level with software plug-ins that have VU meters, although in practice this isn't going to make that much difference compared with -20dBFS


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Re: How to understand a VU Meter correctly?

Postby NT » Mon Oct 17, 2011 7:38 pm

Thankyou Hugh and Martin for your insight into this.

Cheers.
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Re: How to understand a VU Meter correctly?

Postby John Willett » Mon Oct 17, 2011 7:46 pm

Martin Walker wrote:Just to add my two 'pennorth - I've found -18dBFS is a more common reference level with software plug-ins that have VU meters, although in practice this isn't going to make that much difference compared with -20dBFS


Martin

-18dBFS is the European standard, -20dBFS is the US standard.

But Hugh did say "about" -20dB to cover both aspects.
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Re: How to understand a VU Meter correctly?

Postby Martin Walker » Mon Oct 17, 2011 11:12 pm

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Re: How to understand a VU Meter correctly?

Postby Hugh Robjohns » Tue Oct 18, 2011 9:00 am

0VU is the system reference level, and that can be anything the manufacturer wants it to be. In general, most analogue 'studio equipment' opts for +4dBu, but Mackie mixers have always used 0dBu, for example.

the same goes for the digital system reference level. The SMPTE standard calls for -20dBFS, the EBU call for -18dBFS, but other manufacturers use -16 or -12dBFS too. IF you set your monitoring up to the Bob Katz K-System you have switchable references between -20, -14 and -12dBFS, depending on if you're working to K20, K14 or K12 standards.

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Re: How to understand a VU Meter correctly?

Postby NT » Wed Oct 19, 2011 6:46 pm

Thanks everyone,

Am i correct in saying that when the meter shows 0VU on an analog compressor in the digital world it would typically read -18db on a digital meter. On UAD's LA2A Compressor it gives me the option of setting the output level to either +4db or +10db and states a VU meter reading of 0 corresponds to an output level of +4db if set to +4 and +10db if set to +10.

So if i set it to +4 and get the meter to hover around the 0VU mark this gives me an output of +4 so in the digital world would be -14db and the same with +10 it would give me an output of +10 which would be -8db.

I read somewhere that -18db is the best level for recording into 24-bit digital audio systems, as it allows plenty of room for clean transients, if this is the case should i say ie, set the output to +4db and then aim to get the VU meter to hover around -4VU which would balance me up to 0VU and so would get an output level of roughly -18db in the digital world.

Apologies in advance if i have got totally confused with this,

Nick.
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Re: How to understand a VU Meter correctly?

Postby NT » Fri Oct 21, 2011 6:19 pm

Hi chaps,

Was i on the right track with what i said in my last post?

Thanks.
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Re: How to understand a VU Meter correctly?

Postby zenguitar » Sat Oct 22, 2011 12:05 am

Just to let you know, Hugh is away until the beginning of next week but I am sure he'll give you an excellent reply when he returns. He's not ignoring you, I promise, just working away for a few days.

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Re: How to understand a VU Meter correctly?

Postby NT » Wed Oct 26, 2011 12:07 pm

Hi,

Is there anyone out there who could be kind enough to let me know if i was winning regarding reading the VU correctly?

Thanks.
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Re: How to understand a VU Meter correctly?

Postby Hugh Robjohns » Wed Oct 26, 2011 12:33 pm

NT wrote:Am i correct in saying that when the meter shows 0VU on an analog compressor in the digital world it would typically read -18db on a digital meter.

Sorry for delay in responding -- I've been away...

VU meters on compressors are often used to show gain reduction (with 0VU meaning no gain reduction and a reading of -10VU meaning 10dB of gain reduction), as well as output level. But assuming the VU meter in question is switched to show output level, then 0VU probably equates to +4dBu and (depending on the converter alignment) that would probably equate to something like -20dBFS or -18dBFS.

On UAD's LA2A Compressor it gives me the option of setting the output level to either +4db or +10db and states a VU meter reading of 0 corresponds to an output level of +4db if set to +4 and +10db if set to +10.

A lot of people like to drive their compressors hard for effect, and in those cases it makes sense to adjust the VU meter's reference point. Otherwise the needle would be stuck against the end pin all the time! But there is no analogue in a UAD plugin, so the original analogue numbers are pretty meaningless.

In this case, the +4 position appears to read 0VU in the 'output+4' position with a -19.5dBFS tone, and -13dBFS when in the 'output+10' position.

So if i set it to +4 and get the meter to hover around the 0VU mark this gives me an output of +4 so in the digital world would be -14db and the same with +10 it would give me an output of +10 which would be -8db.

The results on my system are as stated above.

I read somewhere that -18db is the best level for recording into 24-bit digital audio systems, as it allows plenty of room for clean transients

Yes. Good advice when tracking and mixing.

...should i say ie, set the output to +4db and then aim to get the VU meter to hover around -4VU which would balance me up to 0VU and so would get an output level of roughly -18db in the digital world.

Broadly, yes... although in pracice I'd suggest it would be better to use the DAW meters to judge overall tracking and mixing levels, and use the plug-in meter to set the amount of compression that you want.

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Re: How to understand a VU Meter correctly?

Postby NT » Wed Oct 26, 2011 8:26 pm

Thanks for your kind reply Hugh, think i understand it a lot better now, if i have any more thoughts will give you a shout.

Many Thanks,

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