Resources for the Recording Musician
August 22, 2007

Effects Order

I have a question regarding order of effects on the stereo output channel.

I have Ozone 3 which is a "mastering" plug in. It contains a graphic EQ, some compressors, reverb, etc. I also have a separate compressor which I like to use to add a little kick to the mix and even out the rough edges a bit. My question is this:

which effect should proceed the other?

It seems like the compressor should proceed the final eq in the Ozone plug in because any changes of added volume with the compressor will want to be seen (and heard) with the Ozone graphic equalizer - otherwise any changes in volume made subsequent to the Ozone plug in will not be seen in the graphic equalizer.

Please let me know.

Thanks again!

First off, you've got to remember that there is no right way or wrong way to do anything in this business.  The only rule is if it sounds good, then it sounds good!  It doesn't matter how you get there as long as it sounds good to you.

With regards to the order of compression and EQ in the signal chain, there again is no steadfast rule.  Sometimes it makes sense to put the EQ first, and other times the EQ last, and other times you may want an EQ before AND after the compressor!

The change of levels/volume by the compressor won't affect the operation of the EQ at all, so I think your reasoning there is a little off.  The only way that could affect things would be if you were driving and EQ hard into saturation and the EQ then might sound different depending on how hot the levels are going into it... then with a compressor you could tame the loud parts and not saturate as much, or you could use the compressor to smooth out the overall volume and then have more room to raise the entire average (RMS) level of the signal driving the EQ.  But, you're really not going to find much of that saturation/overdrive type sound with digital EQs anyway (unless it is a really good physical model of an analog EQ that changes with level instead of using a simple impulse response method).

So, let's discuss what happens when you put an EQ before or after a compressor.

When you put the EQ in front of a compressor, you will change how the compressor reacts to the signal, and, in some situations, the smoothing out effect of the compressor might negate some of those EQ changes a bit.  However, there are many times where you might want an EQ in front of the compressor, especially if you are trying to cut out certain frequencies in the sound that you don't want and that may also cause the compressor to react to strongly.  Once such common use is to filter out the deep low end and sub frequencies from any instruments that you don't want or need that much low end from (typically, you only want the bass drum, and/or bass guitar/synth, to occupy any frequencies below about 80 Hz or so).  Those deep low frequencies have the most energy, and so the compressor will react the most strongly to those, and anytime some heavy low frequencies happen, the compressor will pull down the overall level (unless it's a multi-band compressor, but that's another story).

Typically, though, most people will put the EQ after the compressor because many times they will want to compensate for some negative effects of compression.  Compressors will reduce the attack transients of a signal somewhat (depending on how fast the attack parameters are set on the compressor), which will make the signal seem a little bit duller, and so many times you'll want to add some high frequencies back to the signal to regain some of that.  Also, they can also sometimes muddy up the mid-range a bit, and so you may want to pull out some mids, or low-mids, afterwards to compensate.  Then, as mentioned above, you simply aren't fighting the compressor to get the sound you want if you have the EQ after the compressor.

But, as also mentioned above, there are many times where you will want an EQ before AND after the compression.  When I'm mixing and working on individual tracks, I'll often have a high-pass filter, or low shelf filter, as the first thing on the track to remove the low end and subs from any tracks that don't need to have that (to keep those frequencies open for the bass drum and bass).  Then, if I need a compressor, that will probably be the next thing in the chain, followed by another EQ for sound-shaping as needed.

Likewise, if you are doing mastering of your completed mix, you may want to first put a high-pass filter in the chain to remove any DC offset and deep sub-rumble that you don't want.  A good Linear Phase EQ, such as the Waves Low Band Linear Phase EQ, is good for this.  Then you can do your compression after you've got those troublesome frequencies removed, and followed by another EQ of choice to fix any overall EQ problems with the mix, or to add back some high-end sparkle and air after the compressor has done it's thing.   The very last thing in your mastering chain should be your digital brickwall peak limiter to keep all the peaks below digital zero, and to add some overall loudness (if you wish to participate in the whole loudness war thing that's destroying modern music).  Then after all that is done is when you would dither down to 16 bits for your CD master copy of the mix.

Hope that helps a bit!

As always, thanks for the help.

I had a follow up question.  You state:

"The very last thing in your mastering chain should be your digital brickwall peak limiter to keep all the peaks below digital zero, and to add some overall loudness (if you wish to participate in the whole loudness war thing that's destroying modern music).  "

If one is going to add some loudness after all the EQing, doesn't that adding of loudness destroy all the EQing you just spent so much time balancing?  By adding volume, don't you raise all of the EQ levels?

Thanks again

No, I think you are confusing things again, similar to your question about compressors changing the EQ levels.  A single band limiter will raise the volume of your entire signal by an equal amount.  It won't affect the frequencies you EQ'd any differently.

In reality, what the limiter is really doing is just squashing down, and rounding off, the big transient peaks in your signal, which then allows you to raise the overall volume of the track without clipping the signal.  Most limiter plug-ins raise the volume automatically for you by whatever amount you set the peak reduction to.

To explain in a little more detail, the limiting factor with digital is that once all the bits are turned on "set to 1", there is no higher value you can represent.  So, if your levels exceed the highest value (which we call "digital 0", or 0 dBFS (decibels full scale)), the tops of the waveforms are clipped off with all the values set to digital zero as long as the waveform is above that value... this makes a flat top to the waveform, similar to a square wave, which creates some very nasty digital distortion artifacts (just purposely drive some digital audio signal much higher than digital zero to hear what that sounds like).  What a peak limiter does is to take the highest peaks in a signal and reduce them in level and round them off as much as possible to allow you to then raise the overall volume above what would have normally created clipping.  The soft rounding off of those peaks avoids the nasty clipping type distortion, however, it is still changing that peak waveform from what it was originally, and thus creating its own type of distortion.  In small amounts (no more than around 3 dB of peak reduction) with a good limiter, you won't notice anything other than bringing up the overall volume a bit.  However, if you get caught up in the loudness wars and try to make your audio as loud as possible using one of these digital limiters, then you are reducing the peaks by quite a lot, and the distortion it adds can become quite noticeable... things will start to sound "crunchy" or "brittle", and you might also notice a lack of "depth" to the music, as well as other artifacts.  Thus, it's best to use a limiter sparingly, or to send your mixes to a real mastering engineer who has other tricks to raise the apparent volume level as much as possible while retaining as much musical quality as possible.

Also, the other reason you want to put the limiter last in the audio chain (right before dithering), is that if you do any processing after you limit (such as EQ), then you will probably end up clipping your audio.  The reason being is that you generally are using the limiter to bring your mix right up to digital zero, with as much volume as you want, so there is simply no room to do any additional boosting of frequencies with an EQ without going over digital zero and causing clipping.  Even if you are only going to be doing cuts with an EQ, most filters/EQs still have a resonant peak at the knee of the EQ which will add some gain at those frequencies and again cause you to clip your signal.

So, if there is any one "rule" that is followed in mastering, it's that peak limiting is always the last processor in the signal chain before you dither down to your final output format.


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