In the second part of this two‑part workshop on mastering solutions available to us in Logic Pro, we'll be discussing the use of dynamics processors, as we prepare and polish a stereo mix for the listening public.
Dynamic range is notably absent from a lot of modern music. The argument about losing musical contrast by implementing compression/limiting techniques to make 'gains' in apparent volume is thus complicated by the fact that, to sound stylistically accurate, some types of music will need compressing, while others won't. On the other hand, consider the fact that in order to appreciate that something is loud, you need something reasonably nearby that is quiet. Add to that the questionable value of adding distortion to recordings so that they sound turned up even when turned down (à la Muse), or the 'so loud it's pumping' approach typified by Eric Prydz and we have a debate that will rage on. Assuming you've put your musical objections aside and simply want more level from your track, Logic provides a range of solutions.
Sometimes all you need is a simple compressor to 'glue' the mix together, provide some dynamic control and perhaps impart character to the sound. 'Bus compression' is a term often used for this process, where a compressor is applied to a drum bus, vocal bus or stereo mix bus. The holy grail of bus compressors seems to be those found in SSL G‑Series mixing desks, and in Logic you can approximate this sound by changing the circuit type of Logic's Compressor to 'VCA'.
In a mastering situation, the use of a higher threshold and lower ratio (less than 2:1) is appropriate, with at least 50ms of attack to preserve transients. If you want to experiment, open the extended parameters at the bottom of the plug-in and change the Output Distortion type. Any setting except 'Off' will result in all signals above 0dB being turned into distortion of a type determined by the Circuit Type — and the output of the compressor will not, therefore, rise above 0dB even without the limiter on. This is great for adding a little edge or warmth where appropriate.
If you just need to 'glue' the mix together, a simple buss compressor is the best bet, but if you need dynamic control of individual bands of frequency, turn to Multipressor. At first sight, it has an intimidating interface, but once you realise that it's four compressor/expanders, each assigned to a defined frequency band, it's easier to deal with. Each compressor has a default threshold of ‑15dB, and a default ratio of 3:1, both of which are suitable for mastering applications. Remember that extreme settings in any plug‑in should be questioned at this stage of the production process, as major issues should already have been sorted out in the mix.
Set the number of bands: In its default state, Multipressor is a four‑band device, and while you can reduce its complexity by disabling one or more bands (click the band number), four‑band control is recommended for mastering purposes. This is because specific control of the low‑mid range (often over‑dominant even after mixing) as distinct from the low end (which often requires a bit of support) is crucial at this stage.
Adjust the output of each band: The most straightforward way to approach Multipressor is as if it were a simple four‑band graphic equaliser, using the graphic interface to adjust the gain of each band and its bandwidth. Adjust the output of each compressor, referred to in this case as 'Gain Make Up', by dragging the horizontal lines in the graphic display. Take care, though: any adjustment over 3dB might bring the integrity of the mix into question.
Adjust compressor settings if necessary: You might then consider adjusting threshold and ratio for each band, but make sure you can hear the effect of the changes you are making. You can use the bypass and solo buttons on each compressor to A‑B the effect of adjustments you make, or use the 'Compare' button.
With careful use, this part of Multipressor can be really useful, particularly for adding apparent energy to specific frequency bands without increasing their peak volume and affecting other frequencies.
Multipressor also has an expander on each band. Where the compressor reduces the dynamic range of higher volume levels, the expander increases the dynamic range of lower levels, which can lower the noise floor (counteracting the effect of compression used on its own, which can raise the noise floor!).
Hear what it does: To hear the expander in action, try instantiating Multipressor on a mixed stereo file that has unwanted high‑frequency elements; for example, where the snare part has been ineffectively gated, leaving hiss between the snare hits.
Solo the band: Solo the fourth band in the multipressor and increase the Gain Make Up of the compressor for that band. This will increase the volume of that part of the frequency range, and thus the volume of the hiss between the snare hits.
Expand: Applying downward expansion (by increasing the ratio above 1:1 and setting the 'Reduction' to a negative number) means that each time the signal level falls below the expansion threshold, the gain will be reduced, removing some of the hiss.
Mix back in: When downward expansion is severe, it will sound unnatural, of course, but when mixed back in with the other three bands of Multipressor it can be a powerful tool for cleaning up the mix.
A similar technique can be employed to tighten up the bass end. With the dynamic difference between notes and spaces clarified, the bass part (including kick drum) should sound much more deliberate and leave more space for the mix to breathe.
Although Logic has a separate Expander plug‑in, Multipressor's GUI, allowing you to set compression and expansion thresholds against a meter displaying input and output levels, helps to make sense of a potentially complex combination.
Logic's Limiter plug‑in functions as exactly that: it applies 'brick wall' limiting (that is, compression with an infinity:1 ratio, where no signal can rise above the threshold) without adding any particular character to the sound — but only when used with care! You can perform a visual check on the amount of energy added to the mix when using a limiter by comparing the RMS and Peak levels on the Level Meter. The higher the gain setting on the Limiter, the closer the RMS level gets to the Peak level. Sounds good? Well, maybe not if you increase the gain by more than about +3dB, when the 'effect' of over‑limiting starts to become audible as a kind of pumping sound
The 'Soft Master Limit' preset for the Limiter shows typical mastering values:
Gain set at +2dB: This might not seem a lot, but don't forget that you have already applied significant increases in gain using plug‑ins earlier in the processing chain.
Lookahead set at 7ms: If a final limiter has the ability to look ahead at the digital signal level before processing it, it's pretty much a no‑brainer to exploit this facility!
Release set at 11ms: Usually carefully set to avoid pumping, a short release should not be an issue here if the Limiter is not over applied; remember, it's the combination of plug‑ins that achieves the overall effect.
Output level set at 0dB: There are various schools of thought, and some 'fascinating' discussion on the Internet about final mastering levels. If the material is for broadcast, further limiting will be applied, so over‑compressed material, either with elements of distortion, or lack of dynamics, or both, may suffer as a result of broadcast processing.
None of the plug‑ins listed need have a detrimental effect on the overall sound when used sensibly on its own. However, when used in combination, the difference between 'unmastered' and 'mastered' can be as chalk is to cheese. A little shaping with the Match EQ and Multipressor, combined with 3dB gain from each of the limiters, can bring a track right out of the doldrums and into 'ya face'. There are no real rules as far as plug‑in order goes, except to say that a limiter should come last, to control any unwanted spikes in the final output.
A typical effect chain could be 'Match EQ‑Multipressor‑Compressor‑Adaptive Limiter‑Limiter'. This shows EQ before dynamics, which is common, and two limiters of different character, so that each can be used sparingly, but have a significant effect in combination. However, you may wish to experiment with the order. For example, the difference between running the signal through a limiter before the Match EQ, as opposed to the other way around, may be significant; fewer phase issues may be caused by the EQ in some cases, since relative gain changes will be lower.
As always, the final judge must be your ears. It's very easy to lose perspective during this process and ruin all the good work carried out in previous stages of production, but with care and time it's possible to create satisfying and professional‑sounding results without forking out for expensive third‑party plug‑ins or esoteric hardware.
The Adaptive Limiter functions in a similar way to the ordinary Limiter, but is designed to emulate the sound of a transistor‑based power amp running at high volume. That is, it adds harmonic distortion, which can enhance certain types of musical content, principally simpler rhythmic material, by 'roughening' the edges of transients. This is great for adding a crisp edge to otherwise bland drum tracks. Again, the effect becomes obvious with more than about 3dB of gain, so use sparingly unless you deliberately want to colour your track.
One side‑effect of too much compression could be a slight 'dulling' of the sound, caused by an increase in the relative amplitude of lower frequencies compared to higher frequency transient information. To overcome this, you could try using the Exciter plug‑in, which attempts to recreate or manufacture high‑frequency components using a non‑linear distortion process. Note that we have already mentioned how to create excitement through distortion in two other plug‑ins, so think (and listen) carefully before adding even more!