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AU Peak Limiter
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Jedi Council Member
Picture of Keith
posted
I'm in GarageBand 3, and I have added some Compression to all tracks as well as the Master Track, but there's one spot with a bass drum hit that –kaBOOM!– distorts.

I don't want to turn the volume control on that or any other track down, because then, the rest of the tune won't be loud enough.

Accordingly, I want (I think) to use the AU Peak Limiter. The pre-set paramaters are
.002 secs for the Attack Time
.005 secs for the Release Time and the
Pre-Gain slider is set midway between -40 and +40 dB.

Unfortunately, I don't know what any of that means. What settings would you recommend to increase the limiting amount?
 
Posts: 668 | Location: Dearborn, MI | Registered: October 05, 2002Reply With QuoteReport This Post
Poobah
Picture of Chuck M
posted Hide Post
I can take a stab at this.

You must never record stuff over 0 dB digitally. If you really want to know precisely what all that AU units and dB means, I can't help you. I can give you technical definitions, but I have no idea what's actually coded in GB. Perhaps Apple doesn't either. Considering that the first 10 years of Digidesign's Pro Tools $50K suite of recording tools was all screwed up at fundamental coding levels, it may be possible something is wrong with GB3. It is an entry level application.

I'm not quite sure what your situation is. Is this a synthetic GB drum, or a recording of a real drum? Is this your digital composition, or something you recorded elsewhere (like a once-in-a-lifetime, unrepeatable performance)? You don't mention which GarageBand version you're using; after GB '08, 24-bit recording is possible, if you have the "right" setup (mics have saturation limits too). Is the drum on its own audio track?

You may have only two options (i.e., the first two):
1. re-record the piece
2. live with the distortion
3. splice-in/edit good drums if they're on a separate track

You cannot easily repair drums on a mixed track, analog or digital. If the drums are on a separate track, you could possibly (digitally) hand edit the overloaded section. It will sound funny if not distorted too much, and other sound tracks may help hide it.

Generally speaking, given adequate resources (mostly $$$), in mastering you record at the highest audio resolution possible, which would be 24-bit in this case - and no compression. If your gains are set properly, you would never cutoff-clip-saturate even the highest dynamic range music using 24-bits. "Real world" sounds, like a space shuttle launch could saturate - but not music. (Music is "unreal world," pre-arranged sound Smile). 16-bits is often too narrow a dynamic range - even for unreal world sound. If you record live music, a "live" compressor may be the answer to your clipping problem (as opposed to applying compression in post-processing in a studio with GB). There are different types of compressors, but I'm suggesting a good limiter. You can build one for $50 in Radio Shack parts, or pay a few thousand dollars for a commercial limiter. Caveat emptor. Many commercial "limiters" aren't really limiters at all, and are quite bad. "Try before you buy." Smile A good analog limiter will gently limit the sound from going above 0dB before it is digitized.

I don't know the algorithms GB is using for digital limiting, but they are apparently not working. I have never heard of a good "live" digital limiter, because the coding is exceedingly complex (frequency dependent) and may not be possible in real time. That's why analog pre-filters (like limiters) are necessary in most data acquisition systems, like GB.

Let us know what your next step is. There are measures to take if your answer is re-recording the piece.

This message has been edited. Last edited by: Chuck M,
 
Posts: 2075 | Registered: June 23, 2002Reply With QuoteReport This Post
Jedi Council Member
Picture of Keith
posted Hide Post
Thanx, Chuck. The recording was with MIDI fonts and other sounds I have, and it was not going well, sort of a fizzy sound throughout, so I left the drum distortion in. The wretched result can be heard here.
 
Posts: 668 | Location: Dearborn, MI | Registered: October 05, 2002Reply With QuoteReport This Post
Poobah
Picture of Chuck M
posted Hide Post
OK. Somehow, I read and knew you were using GB3, but I wrote the wrong thing anyway. I guess one can never edit too often.
 
Posts: 2075 | Registered: June 23, 2002Reply With QuoteReport This Post
Jedi Council Member
Picture of Keith
posted Hide Post
The AU Peak Limiter does work, I just wish I knew how to increase its effect. I was also able to improve things by filtering out the thud of the bass drum by using the Hi-Pass Filter on two tracks.

I used to knock GarageBand because of its lack of MIDI capability and those awful Jam Pack sample libraries, but there really is a lot you can do with it in editing sounds.
 
Posts: 668 | Location: Dearborn, MI | Registered: October 05, 2002Reply With QuoteReport This Post
Jedi Council Member
Picture of Keith
posted Hide Post
I was wrong. all the AU Peak Limiter does is chop off the top of the waveform, thus creating severe distortion.

I sure wish I knew what I was doing.
 
Posts: 668 | Location: Dearborn, MI | Registered: October 05, 2002Reply With QuoteReport This Post
Poobah
Picture of Chuck M
posted Hide Post
An AU meter is supposed to "meter" something - i.e., measure something without altering it. Peak meters are famous for detecting peak excursions, but not displaying them sufficiently well.

I don't own GB3, so I can't help you more, unless you want me to drop by.

Once again, how filters and meters actually work, versus their theory, is often the trick required to use such applications. A lot of event-driven (aka, object-oriented) programmers exist in the unreal world of windows & mouse clicks. Realtime control of real physical phenomena eludes their understanding. This problem is made worse by the fact that neither Windows, Mac OS X, or Linux is a realtime OS.

All I'm saying is, you're not alone in your difficulties.
 
Posts: 2075 | Registered: June 23, 2002Reply With QuoteReport This Post
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