Question about using Limiter during Recording

[msr001]

Recently during a recording session, I thought I had everything set as far as levels were concerned. However, when going over the audio later, I discovered that I had a few places where I had clipping issues. So here's my question:

Is it reasonable to set the trims so that recording levels max out say between -6db and 0db and then set a limiter at 0db so that the compression ratio for everything above 0db is essentially infinite? It seems to me that this would avoid having to worry about missing a spike here and there.

[Ethan Winer]

Originally Posted by msr001

Recently during a recording session, I thought I had everything set as far as levels were concerned. However, when going over the audio later, I discovered that I had a few places where I had clipping issues.

I never record through a compressor anymore. Even at 16 bits there's no need to push the VU meter up to the top. So in the future leave 10 dB breathing room and you'll be fine.

--Ethan

[Robert D]

Yeah, it's really not necessary. If you want to put one in where it theoretically should never kick in, then you have to ask yourself if it's presence in the chain is doing any harm. Just because it's not limiting doesn't mean it's bypassed. Your audio is still passing through the VCA or whatever circuit topology it uses, at either unity gain or some linear gain amount. In doing so, it is taking on the sonic characteristics of that circuitry, be that good or bad. So keep that in mind when deciding if it's worth having it in place as an insurance policy.

[Trell Blaze]

In my opinion, I feel that if you must use a limiter coming in, set the threshhold no further than -2db (preferably -3). I feel that letting anything hit 0 is too much and creates more problems than it's worth.

And even so, set your input so that, at it's highest peak, u're only getting 2-3db of reduction. Don't know about anybody else, but that's how I do it when I feel I need to knock some peaks down a bit...

I SOMETIMES throw one on my master bus for songs with big climaxes. Again, I never let the reduction go higher than 2db at the song's loudest points...

Just remember that every song is different (be it recording, mixing, or composing) and rules that apply to one may need to be broken on another...

[steve.h]

Two extremely related questions:

1: if your program says the audio hits zero, but never goes over, is that considered clipping?

2: is the "soft limiting" feature on some digidesign hardware essentially the same thing as the OP described?

[Trell Blaze]

To answer your 1st question, (and I'm sure someone can do this much better than I can but I'll take a shot at it) no...BUT weather or not you can tell if program material actually went over zero depends on the resolution/accuracy of your meters. If it goes over 0 by .1 db it's clipping...and it may not be audible. Your meters may or may not show it. I would advise against taking that chance, but that's a personal opinion.

As for the second question, I don't think I've ever used the "soft limiting" function on ANY gear I've put hands on. Again, this a personal thing - I just don't trust it...

[msr001]

Thanks for the advice. I thought I had at least 3 db of headroom last time, but over the course of the recording session I had a few places where I still went over the top. I guess I might compromise and try and go with about 6 db headroom next time and put in a limiter up around -2 db. Hopefully it will never need to kick in. It seems a reasonable insurance policy to avoid having to go back and rerecord later to try and fix a problem that could have been avoided the first time.

[apl]

Originally Posted by msr001

Thanks for the advice. I thought I had at least 3 db of headroom last time, but over the course of the recording session I had a few places where I still went over the top. I guess I might compromise and try and go with about 6 db headroom next time and put in a limiter up around -2 db. Hopefully it will never need to kick in. It seems a reasonable insurance policy to avoid having to go back and rerecord later to try and fix a problem that could have been avoided the first time.

You can run at -20dB and still have more dynamic range in your signal than will end up in the finished product.

[SouthSIDE Glen]

Originally Posted by steve.h

1: if your program says the audio hits zero, but never goes over, is that considered clipping?

That changes from meter to meter.

The problem is there is no over (let's leave floating point out of this for a moment, guys.) There is only 0dBFS. So the only way that one can surmise that there is probably actual clipping going on is to count how many samples in a row come in at 0dBFS. How many 0dBFS samples in a row it takes before the "Over' or "Clip" light comes on is up to how the meter is programmed.

Many pro studios and gear use meters calibrated so that even one single sample will trip the clip meter. Many (if not most?) pro and prosumer meters, however, consider 3 or more 0dBFS readings in a row to be clipping - meaning one could technically clip for two samples and it would not register; of course you probably won't hear it either. Some meters will even let a full 8 0dBFS samples in a row go by before it indicates a clip, apparently on the theory that you can't hear it until then.

I'd rather not have them make the decision for me. Give me 3 samples or less.

G.

[apl]

Do some ADCs roll over? That is, going over 0 dBfs the signal just keeps going starting at -(0 dBfs)? Maybe that's DACs.

[Ironklad Audio]

here's an idea: set the gains to where you don't go anywhere near hitting 0, thus eliminating both the chance of overs and the need for the limiter

[BrentDomann]

What about setting the input threshold of the limiter to 0dB, setting your compression ratio to something like 3:1, and setting the output level of the compressor to -3dB? You could adjust the ratio and output level as needed, but those numbers would hold down any peaks without crushing your dynamic range (specifically because you're not increasing the input level). Plus, at -3dB and 3:1, you'd have to have a hell of a peak to clip.

[Trell Blaze]

Originally Posted by Ironklad Audio

here's an idea: set the gains to where you don't go anywhere near hitting 0, thus eliminating both the chance of overs and the need for the limiter

Noise floor should be taken into consideration here. Personally I like to eliminate as many db's as possible...

[89gtsleeper]

I am scared of limiters because of the way they change the sound sometimes. What I would prefer doing in your case is lowering the input gain just a hair (maybe a few db), then mildly compressing from a failry high threshold just in case... fixed.

[SouthSIDE Glen]

I know this is a stale thread already, but FWIW I have a whole new interactive app on metering and gain structure up and operational on the IRN website. Just click on the logo in my sig to get to the site, and then click the logo for "Metering and Gain structure."

G.

[Tim Gillett]

I think the only normal reason for using some form of compression on record would be because your converter's signal to noise was being exceeded by, or likely to be exceeded by, the dynamics of the signal. I dont think too many would disagree that the distortion of a good soft knee limiter is far preferable to the distortion of clipping. Both introduce distortion but what is the lesser evil?

In the earlier days of analog tape this was a common situation. Recording of say a concert in front of a live audience meant a potential dynamic range way in excess of the recorder's abilities. You couldnt tell the orchestra or band to stop half way through so you could redo the track with lower gain settings. You only got one chance.

In some of his legendary Nagra field recorders, Stefan Kudelski built in not one but two limiters, both of which could used or defeated independently. One of them gave a readout in db's of the degree of limiting. With certain types of undemanding live recording, you could get away with no limiting, but with other more raw, unpredictable material only a fool would record without the safety of the limiter, unless you wanted to try your luck at gain riding. But then you needed to know how to use the limiter correctly.


I think many people can be unaware a vocal track has been compressed a little, but most people know something's wrong when they hear hard clipping.

If I had to choose between consistently and audibly going over 0dbFS and avoiding it using a good limiter, no choice. The lesser evil principle.

Tim

[Gandalf]

Originally Posted by SouthSIDE Glen

I know this is a stale thread already, but FWIW I have a whole new interactive app on metering and gain structure up and operational on the IRN website. Just clisk on the logo in my gig to get to the site, and then click the logo for "Metering and Gain structure."

G.

That's great Glen......

[TexRoadkill]

I only use a compressor or limiter if I want their sound or I'm doing live concert recording. I usually try to peak around -12db when tracking.

[The Axis]

I am of the opnion that there is no need to push close to the danger zone. Who cares if your sound never goes above -1 dB ? You will never hear the difference. But if you go over, or start using heavy compression, it wil definitely change the sound.
Of course, maybe you like very high compression. That is OK too. If you can't hear the overshoots, then it is OK for you.