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Topic: Clipping and Compressor Usage
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Posted On: Aug. 23 2006, 2:00 AM
TomM
 

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Hello,

This is my first post, and I appreciate any help that is offered!

I am recording an accordion, which has a very wide dynamic range.  I am confused about the best way to go about setting the volume for the mic.  From what I've read on this forum, I should try to maximize the volume into the red range, but avoid actual clipping.  I find this rather iffy and am sure there must be a better way.

I thought maybe I could use the compressor to compress the highs somewhat, but if I should, when do I use it?  That is, should I record without using the compressor, and then apply the compressor later as an "editing" tool?

At one point, I thought the "normalize" function would do the trick, by simply setting the maximum to some level and then allowing the program to recalculate the wave file.  However, the more I've tried to "study" this, the more confused I have become.

Perhaps someone could recommend some good articles that would help me to sort this out.  I am wide open to suggestion, and I appreciate any help that is offered!

Thanks!

Tom.
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Post #2 Skip to the next post in this topic.
Skip to the previous post in this topic. Posted On: Aug. 23 2006, 2:51 AM
Captain Damage
 

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If you're recording at 16bit you should try to get your levels high without clipping. For a dynamic instrument, try to get them mostly in the yellow, only occasionally jumping briefly into the red. It will take a few tries to get find teh right input level. If you're recording at 24bit (i.e., you bought a special 24bit audio interface and paid extra fro the 24bit version of n-Track), then you can record with a "safer" (lower) level where clipping is not a possibility.

Stay away from "normalize." It almost never helps anything.

Record without the compressor or any other effets/plugins. After you've recorded the track, use the track EQ. If your mic has added any coloration or tone you don't like, try and EQ this color out and make the track sound as natural as you reasonably can.

Now add the compressor. The way a compressor works is to reduce the volume of the track by a ratio amount whenever the track exceeds the threshold level. This allows you to bring the quieter parts up without causing the louder parts to clip; you are compressing the dynamic range. One of the main reasons you'd want to do this is to help a dynamic instrument (or voice) sit more evenly in the mix. In a full mix a single dynamic track often sounds alternately too quiet and too loud, never just right.

Unfortunately, because the behavior of compressors is dependent on how often the track crosses the threshold - which will be different for every track - it's very hard to give blanket recommendations about settings (many compressor plugins I've seen don't even have presets programmed in). But as a place to start, try a ratio of 4:1 and a threshold of -9dB (I'm guessing you recorded mostly in the yellow which is centered at -9dB). Play with lower and higher thresholds and greater and lesser ratios. Compression can be made to sound like an effect or it can be subtle and virtually transparent. You have to play with it and get a feel for it.

Hope this helps!
KRL
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 3:22 AM
TomS
 

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Compressors are used for lots of things, including what Capt. D recommends (although I'll bet you'll find that a ratio lower than 4/1 will be the ticket).  They can also be used as limiters at the time of recording, which can really help get hot signals - and I'm certain that I am wrong about this, but even with 24/96 or whatever, hotter signals always sound better to me.  So if you have the option, you might try a (hardware) limiter going into the soundcard, just to make sure you catch any overs that might creep in, and try to get as much as you can.  

For myself, I like to hear the dynamic range on the instrument, especially if it's solo.  Putting accordion in a mix might require a lot more compression to get it to sit.  But I've always loved accordion; put it in a nice room with a nice mic or two not too close to the instrument and let it rip.  :)

Hey folks, TomM was the 2006th registered forum member, doesn't that numerological coincidence entitle him to some free plugins or something?  :D
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 3:25 AM
TomM
 

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Thank you, Karl!

So, a few questions come to mind...it sounds like I should upgrade to the 24bit version of n-Track.  I am using an M-Audio USB Duo, which I believe is 24bit capable.  I don't really understand how this would reduce/eliminate the clipping, but it sounds like a good way to go.

I should add that what I'm doing is pretty simple.  I'm recording myself playing the accordion into a single mic (AT3031), so I end up with one single track (I suppose I should have bought 1-Track!!).  Clipping has been a problem for me (I assume because of the wide dynamic range).  I want to make these recordings for my Mom, and I don't want any artificial harshness in there.  She likes what I've done for her, but that's because she's my mother!  (I hear little bursts of harshness that I don't like, and which I assume originated in the clipped wave file.)

So, Karl, are you saying that if I use the 24bit version of n-Track , I won't have a clipping problem to worry about?  That sure sounds like the way to go.

I am totally new to the compressor, so I will take your advice and play around with it.  The key thing you've told me is to record without any effects.  By the way, the compressors I have available are the one that came with n-Track Ver. 4.2.1, and the Kjaerhus Audio Classic Compressor (which was recommended in one of the posts I read in this forum).  Which would you recommend?

Thanks again for your help!

Tom.
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 4:03 AM
TomM
 

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TomS said:
Compressors are used for lots of things, including what Capt. D recommends (although I'll bet you'll find that a ratio lower than 4/1 will be the ticket).  They can also be used as limiters at the time of recording, which can really help get hot signals - and I'm certain that I am wrong about this, but even with 24/96 or whatever, hotter signals always sound better to me.  So if you have the option, you might try a (hardware) limiter going into the soundcard, just to make sure you catch any overs that might creep in, and try to get as much as you can.

Hi, TomS!  Thanks for your input.  As I said in my previous post, I have very little experience with using a compressor, so I'll have to play around with them.  Sorry, due to my inexperience, I don't even know what a "hot signal" is, and what it would mean in my situation.  Perhaps you could say more about this.  I don't have a hardware limiter, so I can't try that idea.  My setup is very basic...just a mic going into the Duo, and the Duo feeding into my computer.

TomS then said:
For myself, I like to hear the dynamic range on the instrument, especially if it's solo.  Putting accordion in a mix might require a lot more compression to get it to sit.  But I've always loved accordion; put it in a nice room with a nice mic or two not too close to the instrument and let it rip.

As I mentioned in my other post, I'm playing solo and making simple recordings for my Mom.  I actually am very pleased with how it's going so far, but this clipping/distortion issue is something I'd like to learn to control.  And, like you, I really enjoy hearing the complete dynamic range, from ppp to fff.  Being a neophyte at this recording business, it seems to me it will be quite a challenge to capture all the dynamics.

Hey, I like your idea about the free plugins!  Only one problem...at this point in my recording career I probably wouldn't know what to do with them!   :D

Thanks again for your input, Tom!

Tom.
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 2:30 PM
Captain Damage
 

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So, Karl, are you saying that if I use the 24bit version of n-Track , I won't have a clipping problem to worry about?  That sure sounds like the way to go.


Recording at 24bit will allow you to retain high resolution (audio quality) at a lower input level. So you can record at a safer level, staying out of the red alltogether without being worried about how close you're coming to clipping. At 16bit you generally want to record as hot as you can without clipping to get the maximum resolution. To get a little more technical, the lower the input level, the fewer bits you're actually using to encode the sound. So while a low level at 24bit might still be using 16bits, the same level at 16bit would only be using 12bits.

I'd work at 16bit and get used to recording correctly before springing for 24bit - just my $0.02
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 4:11 PM
TomS
 

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Well, a "limiter" is a compressor with a high ratio setting - 10 to 1 or greater is the standard definition, I believe.  They are often put in line between the preamp and recorder to make sure that signals that are too "high" (or "hot") don't cause clipping.  Theya re also used in other contexts - e.g. to protect speakers in high volume settings like concerts.

The concept you need to think about in this regard is "gain structure."  Think of all of the separate steps in recording - typically: the sound comes out of the instrument, goes into the microphone, if it is a condensor mic it will have some electronics in it that will amplify the signal a bit, then it goes into your preamp, then into whatever external or "outboard" processing you want to apply to the signal before it is recorded (e.g. limiting or compression or EQ or whatever) and then into the recorder.  At each step the level in must be correct, and the level out as well (so that the level into the next step is correct).  So you can get clipping at the mic, in the mic's electronics, at the preamp, at any outboard processing, at the recorder (e.g., the digital converter, which is where you are having problems) and (if one is recording to tape) at the recording head on the tape ("tape saturation").  Not all of this overloading is necessarily bad - most rock records are recorded pushing the preamps, and they used to be recorded with tape saturation often enough, and still are when tape is used.  But that's not what you want, not right now - you want a clean representation of your playing.  So...

Your mic is a really nice mic, and the m-audio duo I've heard is also great, I know that it has a 20 db pad on it and a clipping indicator, so gain structure should not be a problem at all.  Personally, I'd go register the 24 bit version and do exactly waht Captian D. said in his first post, but he has a really good point about learning using 16 bits first.  But I'd still go for the 24 bits.  It's not like it costs very much, and you will get all the extra headroom from 24 bits, plus better sound from the 96 sampling rate.  

The other thing i'd think about is getting a second 3031, 'cause if you have a nice sounding room (living rooms often work pretty well!) then you can get very natural stereo recordings (but note that there are placement issues when you are working with two mics, b/c they can cause comb filtering due to phase cancellation - which means exactly what it sounds like it means, some frequencies can be cut and others enhanced and the result is often unpleasant - so if you decide to do this, you might want to look at some of the on line lit on mic placement - DPA microphones has some great general articles on this, featuring  their mics of course, but still useful).   I'll find the link, but it used to be under dpa mics "microphone university" - which had an article about placement for recording accordion, I do believe.  :D
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 4:20 PM
learjeff
 

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It's really very simple.  If you're getting clipping, reduce the recording level a bit and try again.  Repeat until you can record without any clipping.  Bingo, done.

When recording at 16 bits, you generally want the resulting recording to peak at -12dB or higher, because every 6dB below 0 essentially wastes a bit.  So, peaking at -12dB, you really have a 14-bit recording (which, despite all the arguments, is still a very good recording).  But 13 or 12 bits?  You're starting to suffer.

With a 24-bit recording, if you waste a couple bits, you still have plenty left.  Enough so that you no longer need to think in terms of wasting bits, and instead worry about the analog noise floor of your mic preamp and A/D converter, and then only for signals with rather low levels.  For example, recording a piano solo that ranges from ppp to FFF, the ppp section will be very quiet.  My suspicion is that an accordion part doesn't generally vary in volume quite THAT much, and you should be quite OK.

PS: Captain, your idea is right but your math is wrong.  If you're peaking at -48 dB, you'd get 16 bits on a 24-bit recorder (if it really recorded 24 bits, but they don't) or 8 bits on a 16-bit recorder, not 12 bits.

Cheers
Jeff
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Skip to the previous post in this topic. Posted On: Aug. 23 2006, 6:15 PM
TomM
 

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Karl, Tom, and Jeff:

Thank you all for your contributions.  I'm printing this off and I will refer to your guidance quite often.  

Karl, putting all the comments together, and trying to understand the difference between the 16 and 24 bit recording (which I do not yet understand), I'm thinking I'll upgrade to the 24 bit.  I get the sense that it "can't hurt."

I'd like to understand the 16 bit/24 bit thing better.  Can you guys recommend any reading for me?

Tom, about the 2nd mic, and recording in stereo...I have done some experimenting with this, and have (for the present time) decided I like the sound I get using only one mic.  That's not to say it's "better"...just a personal preference.  There has been some debate about this within the accordion community.  

What I've been doing is placing the mic about 3 to 4 ft. in front of the accordion, but aimed at the treble side.  The bass side is still captured with this arrangement.  Then, as recommended to me by an accordion friend, I have cloned the track, panned the two tracks a little right and left, and combined into a stereo track.  Not very sophisticated, I admit, but it seems to make a nice sounding recording.  My Mom (90 years old, bless her soul!) thinks I'm right in the next room playing for her.

Of course, I would like to learn how to make my recordings better and better as I go along.  I've been reading the n-Track User Guide, but I think I find more helpful answers right here on this forum!  (Not to say the User Guide isn't a good thing!)

Thanks again for the help!  You guys are great.    :)

Tom.
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Post #10
Skip to the previous post in this topic. Posted On: Aug. 23 2006, 7:08 PM
jwgeetar
 

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wow---yes good stuff! i never realized that you actually used up bits till i read this. so by having 24 bits as opposed to 16, one is pretty much in la la land without having to worry about sound degradation. right? ???
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