Boss BC-1X: The new BC-1X is a digital multi-band compressor designed for bass. It's been a long time since Boss brought anything new to this category, so we are all quite excited.
With multi-band compression, your signal is divided into separate frequency ranges (bands), and each band is processed separately, and then recombined at the output. This means large peaks in the lows will not trigger compression of the mids and highs at the same time, so it will not "swallow" those frequencies the way a normal single-band comp does. This results in brighter, cleaner tone and articulation. Each band requires its own compression circuit, so it can get expensive in the analog realm, which is why analog units like the Ashdown, EBS, and FEA are only dual-band. So it makes sense that Boss went digital for this one--though they do not specify how many bands the signal is divided into.
In fact they do not provide much information about the inner workings of this unit. The website says "Hidden behind the pedal's simple four-knob interface is a complex multiband processor with numerous interlocking parameters. As you turn the knobs, many parameters are adjusted at once". Yet the knobs include Level, Release, Ratio, and Threshold, which are fairly straightforward about what they do, and we can't assume which other parameters would be adjusted automatically as you turn those four. Maybe the Release knob also affects the attack time? Maybe the Ratio knob also affects the knee? Maybe they decided a higher ratio should have a faster attack? Who knows. But on the other hand, maybe that is not important to the end user, who only cares whether it sounds good and works well. So does it?
The multi-band processing works exactly as it should, with the bright articulate sound I mentioned. The noise level is very low at most settings. The tone overall is neutral, not fat but not quite transparent either, with no loss of highs or lows. The action is smooth and even, without dipping or other squashy effects. It is common with multi-band units for the low end to sound tighter and perhaps less powerful than other compressors, because the higher frequencies are brought forward in the mix, and that is true in this case as well. It is also common with real-time (not look-ahead) digital compressors that they have some difficulty controlling big low frequency peaks, allowing some spikes to pass through; and that again is true with the BC-1X. Both of these problems with the low end will depend on your settings, and the signal you feed into it.
Generally I found that I got the most natural and full yet controlled sound with the Ratio set around 12:00, for pretty much all playing styles. I was not able to get it to work well as a peak limiter (high ratio) with long sustained heavily-plucked low notes; either they sounded weak, or they caused distortion later in the chain. With other comps, a setting I would normally choose for fattening and sustain is a low ratio and a low threshold, but here the BC-1X sounded more processed rather than fat. However it helped keep all the notes at around the same level, so this is useful for instruments that have uneven volume from string to string. Where the effect really worked exceptionally well was with slap and pop playing. Those shorter bursts of sound, quickly jumping between high and low notes, were easily kept in check, allowing more consistent volume without the tone suck of a typical compressor.
It has a row of LEDs that indicate the amount of compression, and this meter is very responsive and easy to read. The 9V power is boosted internally to 18V for greater headroom, meaning less risk of distortion from high-output basses. Boss is known for reliable construction quality, though I don't know if any new digital pedal will last as long, or take as much abuse, as their old analog pedals. The housing, the bypass footswitch, and the powering are all the classic Boss standard.
The nearest competitors are the MXR M87 and the EBS Multicomp. The MXR has warmer, fuller tone, while the Boss has crisper articulation, and the threshold control of the Boss is much easier to dial in than the input level knob of the MXR. The EBS has its "Tube Sim" mode for warmth, and its dual-band mode for articulation, but the Boss has much better LED metering, and higher headroom, plus a release time control that the EBS lacks. The EBS has internal trim pots for tweaking its multi-band response, but the Boss does all the tweaking automatically. For fingerstyle playing I prefer the sound and action of the MXR and EBS, but for slap and pop I think the BC-1X did the best job of controlling the levels without stifling the tone. If you use a pick, the Boss will make that sharp pick attack cut through even more.