Rane DC 24: This one has long been known as a favorite among bassists. It is a two-channel line-level rack unit with an excellent crossover built in, so it can be set up as a dual-band processor. This allows it to compress the highs or the lows independently, only affecting the frequency range that actually needs it. This prevents "drop outs" of your signal when a big bass peak hits, by allowing the highs through uncompressed. Because of this it is very good for a consistently articulate sound across the entire fretboard, as well as being good for heavy hitters who need to keep a lid on it while still sounding somewhat natural.
There is barely any noise at all, and no rolloff of the highs or lows, although the low end is not quite as "big sounding" relative to the highs and mids, compared to some other comps (this is common with multi-band compression). The crossover point has no artifacts that I can hear, although different settings will affect the way the lows and highs are heard, like using an EQ. The overall tone is very transparent. The limiter function is pretty decent, and not especially prone to "pops" or other artifacts.
The expander/gate is fairly hard to figure out, and that limits its usefulness. However it does work well, and at low ratio settings it sounds more natural than the gate on the dbx units. By activating the gate only on the high channel, you can gate hiss and high-pitched background sounds without impacting the lows, which is pretty cool. I wish this unit had attack/release controls instead of the expander/gate, but even so, the fixed attack and release settings happen to sound great for general bass usage.
This unit only works with line-level signals, it is not meant to take a guitar or bass plugged in directly. Its meters are only accurate when given +4dBu line-level input. That said, you can use the "Trim" switch on the back to set it to work with some lower-level signals, like preamps or effects loops with low output, by selecting the -10dBV setting.
It does have a lot of non-intuitive knobs and switches, so it's not easy to set up; but the results are well worth the effort if you are interested in what a dual-band comp can offer. For example I compared it directly against the Symetrix 501 and a few dbx models, and found that those are much easier to dial in with a good tone and useful settings, but they just can't do what a multi-band compressor can. To illustrate, playing loud low bass notes -with the low EQ boosted- into the 501 and the DC24 really shows their differences: the 501 will clamp down hard on the whole signal, resulting in a big bassy dub tone with minimal highs; the DC24 will clamp down only on the lows, giving a more "tight and controlled" sounding bottom end, and allowing plenty of upper frequencies and finger articulation sound to come through. Each of them sounds awesome in their own way. With a normal, less exaggerated input signal, the difference is less obvious. The DC24 has a better limiter than the dbx and Symetrix units; also its high frequencies are smoother-sounding than the 501 and brighter than the dbx units.
To use it as a one-channel dual-band compressor as I've described, set it up like this:
Line-level output from a preamp into "CH.1/Crossover In" jack. Use either XLR or 1/4", not both (no mixing).
"Crossover Engage" switch in.
"Separate/Combine Outputs" switch set to combine.
"CH.2 High/Combine Out" jack into your power amp, mixer, or effects-loop return jack. You can use both 1/4" and XLR outputs at the same time if you want.
There are six "Threshold" knobs: each channel has one for the gate/expander, one for the compressor, and one for the limiter. Set the gate threshold on both channels to maximum, so that it does not do anything at all. Leave it that way until you absolutely have a need for gating or expansion. For the compression thresholds a good starting point is where the LED for each band lights up for about 50% of the time that you're playing. This lets you know the comp is engaging, but not too much. Set the limiter thresholds at maximum, fully clockwise; then gradually bring them down until just the loudest peaks from your signal light up the limiter LEDs. From there you will be able to adjust everything to your own taste.
For bass, set the crossover to 125 Hz or lower. Even the lowest setting, 70 Hz, is very useful.
You can also set it up to split the signal, send it to separate outputs for separate processing, and then recombine the signal into the DC24 and out the CH.2 output jack. The manual explains this and other details, and it can be downloaded from Rane directly: http://www.rane.com/pdf/old/dc24man.pdf.
NOTE: Their DC22 model does not have the dual-band/crossover function. It's fine as a two-channel full-range compressor, but it is not a substitute for the DC24.
Price in USD: used $75-$250, no longer available new.
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