Most engineers use a degree of compression with bass guitar, which is a good idea for a number of reasons. If the player uses a slapping or pulling technique, the note attacks can be very loud, so if you don't compress or limit, you either run the risk of overloading the recorder or you have to set the record level so low that the main body of the bass sound is too quiet.

This type of playing is best dealt with using a compressor that has a separate limiter, as the traditional way of making a compressed sound retain its attack characteristics is to set the compressor attack time to several tens of milliseconds in order to allow the initial transient to get through uncompressed. The release time is generally set to around a quarter of a second, but this will vary from model to model, so always experiment. Auto-attack and release settings (where available) also produce good results on bass guitar as they can adapt to the changing dynamics of different playing styles within the same song.

Allowing the transients to sneak past the compressor might produce a great sound, but it's those same transients that cause recorder overload problems, so having an independent limiter section following the compressor is very desirable. The limiter threshold should be set just below the overload level of the recorder so that limiting takes place only on very loud peaks.

Even if the bass is played in a more traditional way, compression is still beneficial as it evens up the levels of different notes and, equally importantly, it increases the average energy level of the sound -- making it seem louder for the same peak level. You can still back off the compressor attack a little to accentuate the start of the note, but keep an eye on those recording levels.

A useful tip if you don't have a compressor with a separate limiter section is to use a dual-channel compressor and feed channel one's output into channel two's input. Set channel one up to compress as normal, but set channel two to limit by using the highest ratio possible combined with a fast attack time and as fast a release time as you can get away with. Adjust the threshold of channel two so that gain reduction only occurs when the level is within a few dBs of hitting the overload region on the recorder's meters. Of course those still using analogue tape can afford to be that bit more casual about levels -- indeed, a little tape saturation can do wonders for a bass sound.

"If you don't use compression and you want your tunes get played by sound systems it's going to sound horrible and muddy. Compression on bass and kicks is very important. Try settings like fast attack halfway release and 6 or 7 to 1 ratio depending on the strings and or tubes used.

A couple of years ago I was forced not to use a compressor because of a too small wallet. So there were some labels that were going to release my tunes but they asked for new mixes because of the bass and also I got complaints from sound systems that played my tunes that the bass was too muddy” Stonelion said in a mailing list.

The following are suggested settings for bass compression for initial setting reference to event out inevitable level variation of bass guitar when played over a wide range. Since the equipment spec varies, feel free to tweak them or follow manual guide of respective product to suit your best sounding judgments.
Threshold: 9-12 dB
Ratio: 1 o’clock
Attack: 2 o’clock
Release: 3 o’clock or auto

ART Tube Pac Microphone Preamp and Compressor (Model 131) $199.95
The Tube PAC from ART is a combination of the world's most popular tube mic/line preamplifier and optical tube compressor. Also serves as Tube DI Box!
The mic/line preamplifier stage is that of the TEC nominated Tube MP-a time (and studio) proven design. It provides over 70dB of gain, +48v phantom power, phase reversal, and is capable of warming up any instrument or microphone. LED level indicators are provided to monitor the output of a 12AX7a tube for harmonic content.
The tube compressor is a VCA-less, optical design-similar to that of the classic tube compressors. Its ultra-musical sound is ideal for voice and instrument applications. Threshold, compression/limiting ratios, adjustable release times, bypass, gain reduction metering, and output gain controls are provided.

Behringer MDX2600 Composer Pro XL Processor $109.99
Whether you're recording, mixing, or mastering, the Composer Pro-XL MDX2600 gives you total dynamic control.
Features:
Switchable IKA (Interactive Knee Adaptation), Integrated de-esser
IGC (Interactive Gain Control), Switchable dynamic enhancer, IRC (Interactive Ratio Control), Tube simulation, Automatically or manually adjustable attack and release times, Low contour filter, Stereo couple function

Alesis 3630 Compressor $99.95
The 3630 Compressor is designed as a high-quality, versatile compression unit which can be used live or in the studio with consistent results. The 3630 is a dual-channel compressor that offers Ratio, Threshold, Attack, and Decay controls to handle the toughtest signals. You can choose between RMS and Peak compression styles, plus Hard and Soft Knee dynamic curves for every application from subtle gain control to in-your face punch. Plus, 2 fully independent gates give you even more control when dealing with difficult signals. Other advanced dynamics processing features such as precise signal metering, a sidechain for keying or ducking effects, and stereo linkable operation make the 3630 the most powerful compressor in its class.