Whether you're making pop, rock or dance music, bass is the anchor of your tune. It provides rhythm, groove and lays the foundation for the rest of the mix to be built upon. Producers often run into issues with bass. Not only is bass difficult to monitor in a reliable way in most home studios, but certain attributes of the sound itself can cause problems. Much like when dealing with drums (see These Are Your Drums on Compression), producers reach for compressors when processing their bass for specific reasons. Compressors can be used to reduce the dynamic range of a bass performance and level out of the differences in volume between hits. Compressors can also be used to accentuate or reduce the punch of bass sounds. When working with bass sounds comprised of multiple different voices layered together, a compressor can help glue them together to make the bass a single cohesive mix element.
In this article we're going to look at the dos and don'ts when it comes to compressing your bass and some strategies you can apply to your own mixes. If you haven't read our previous articles on compression and you like to do things in order, check out Part I and Part II of the series.
Compression is often useful when working with bass guitar because inconsistent note volumes can lead to some notes overwhelming the mix and other notes dropping out of it. Compressing the louder notes will allow for a more consistent output level of the bass and help make the bass easier to mix.
Smoothing Out Note Volumes
Smoothing out note volume doesn't require copious amounts of compression and for this purpose you don't need a crazy fast compressor set in peak mode. For this example, I set Compressor to RMS mode, so the compressor is a little less sensitive. I started with a ratio somewhere between 2:1 and 4:1, an ultra fast attack and a medium release and a threshold set to 'way too much.'
Most electric basses have a pronounced transient at the front of the waveform that provides the pluck sound of the bass. Generally this transient is considered a good thing because it adds impact to your bass. To preserve it, use a slower attack time will be required. Start increasing the attack time while listening for the pluck sound to come through uncompressed. Once you have the pluck sounds coming through adjust the release time. Similar to drums the release will need to be fast enough to recover in between notes but not so fast that you hear a "sucking" sound from the compressor. The idea is to clamp down and release the compression relatively quickly so that the tail and sustain of the note will still be audible.
Fine tune the threshold and ratio settings. To smooth of the volumes of different notes in a transparent way somewhere between 3 and 5dB of gain reduction is plenty. Compensate for the gain reduction and set the output gain to match the uncompressed signal. A/B the processed and unprocessed signals in the context of the mix to determine if the effect sounds better or not.
Unlike electric bass synth bass doesn't often NEED compression. Amplitude envelopes can easily be adjusted to sculpt transients and control the sustain. Note to note volume differences can be eliminated by turning velocity sensitivity down, or off. Often producers will apply compression to synth bass out of habit (bad) or to add tone of colour to the sound (good).
In this example I made a simple patch with Operator a coloured the sound with a compressor:
I set the ratio to 3.82:1, an attack of 5.99 ms and a release of 41.1 ms. I set the threshold so I'm getting around 4dB of gain reduction. It is really quite subtle but the compressor adds a little bit of warmth to the sound.
SMOOTH OUT VOLUME CHANGES INTRODUCED BY MODULATION
Another option would be to smooth out the volume caused by modulation on the bass. I took the same patch as the previous example but controlled the filter cutoff with an LFO. Because the filter is rolling off the high frequencies of the sound a perceptible volume dip is introduced. To smooth things out I added a compressor in RMS mode. I set the ratio to 2.63:1, the attack to 31.1 ms and the release to 73.9 ms. I set the threshold so I get around 3dB of gain reduction.
Just like with drums sounds, layering of bass sounds is a common electronic music production technique. The idea is to have 2 to 4 different layers that are responsible for distinct frequency bands. Commonly, a producer would separate the sub bass, mid bass and high bass. It's a powerful technique because it allows you to design incredibly rich, textured sounds and process the composite layers separately. For example, you could apply distortion or stereo effects to the mid and high layer of your bass sounds without destroying the sub. The down side is sometimes the layers will sound like multiple instruments when you want to them to be perceived as one instrument. To solve this issue, you need to process all of the layers at one time. A glueing effect can be achieved in a few different ways but, EQ, distortion and compression are the most common tools. If you plan on using compression to achieve the glueing effect, a gentle squeeze with relatively slow attack and release is all you need.
For this example I used an Instrument Rack to layer three different Operators together and processed the output of the Rack with an Auto Filter, Reverb, EQ Eight and Glue Compressor.
I started with a ratio of 2:1, an attack of 10 ms and a release of 0.6 ms. I turned Soft Clip and applied 5.08dB of Makeup gain to overdrive the signal. The signal is hot enough going into the compressor I only brought the threshold down to -09.5dB to achieve 3-4dB of gain reduction.
As is always the case with compression, only compress if you have a reason to do so. With bass often producers treat Bass Guitar differently than Synth Bass. Bass Guitar is often plagued by inconsistent note volumes and needs to be smoothed out in most genres to provide a solid foundation for the rest of the mix. This smoothing out of note volumes can usually be achieved with pretty mellow compression settings. When you're dealing with Synth Bass compression try turning the velocity sensitivity off so you won't have note to note volume differences. If you do this, you probably won't need to use compression unless you want to add tone or smooth our volumes changes caused by modulation. Normally aggressive compression on synth bass isn't required. When you're layering different bass sounds together compression can be used to glue them together so they are perceived a one sound.
More more information on compression and how to use it check out our Mixing and Mastering class taught by Tim Allan.
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