jb90

I do both. I find engineers are increasingly less fussy about gear but I try and stay traditional. Having it set up well for you and intonated is a must. If anything gets commented on frequently, it's tuning. 

Certain songs will demand a 5, or it will have been used on the demo and they really want those low notes, so keep a 5 on you. I personally find a PJ5 will get me through anything and always start there. I will bring a Fender P with flats and a Jazz too, but 9/10 times I'll start with the PJ5 and everyone will be happy with that. 

I have a small tube amp I often bring along, but most of the time it's direct to save spill to the drums, and I run an amp sim from my Helix or VT Bass DI alongside a clean Avalon U5 or Warm Audio WA12. 

Most important is to bring a good vibe to the room, and try and get things done as quickly and efficiently as possible. Make sure you know the arrangement and anything else you need to know before you sit down to track the parts, whether that's live multitrack, or just you in the control room with a producer. Give them some takes that are rock solid and sound great. if you've got those down but hear something in playback that you think you could add something special, don't be afraid to let them know - it may be wanted or it may not. Let your ideas flow and come across, but also be aware that sometimes, they're not wanted or not in their vision for the track.

Most of all, have gear that works, is reliable, you know, and doesn't hinder your playing. Make their tracks sound as good as you can, and try and sprinkle in that moment of brilliance that they didn't know they were missing - you won't be forgotten in a hurry!

Good points above.

Rule number 1 - don't be an ******* !

Most of my work these days is behind the desk rather than in the studio, and unless the band/bassist has a very specific tone in mind that a certain amp gets them, I quite like to go direct. That is often the basis of a sound that sits nicely in a mix. Almost everytime a player switches on a Sansamp, or tweaks an amp or what have the bass sounds great in isolation, but completely disappears in the mix! And it often just muddies the mix up.

Of course, if the bass - and a specific sound - is a driving force in the song, then anything goes.

But as a session player, a couple of solid basses is good, but above all be on time (both musically and punctually!), in tune, take interest in the songs you're playing and, crucially I think - DON'T BE TOO PICKY! If the artist and producer are happy, then so should you. By all means point out anything that really bugs you and want to re-do, or a different part you think might work well, but if the clock's ticking you won't get asked back if you take an hour obsessing over one fill!

Last week I had a session double bassist in the studio, and he did all his parts for an album album in around 3 hours (over two days). He was a fantastic player with a great sounding bass, but also a lovely guy with no ego, despite having done sessions for some fairly big names. He was a pleasure to work with, took directions where it was given, and was also happy to try things out when asked.

Whatever you do, try and make it enjoyable for everyone!

Everything said above is great advice. I'd add to that by saying, and it depends on the specific needs of the session of course, but as always, less is more. Getting too busy is probably not going to work for most situations. And messing around up the dusty end is a no-no too (unless they ask you to, of course). Somebody once said that the money is made in the first 7 frets. As always, we are all here to serve the song, don't lose sight of that.