Even that's not needed. Especially if you use a converter with built-in preamps. Simply adjust the preamp level so the digital audio never clips. It's that simple.
--Ethan
Ethan, while I have a lot of respect for you, I am going to have to disagree with this statement, simply because in my experience with my equipment tracking close to 0dBFS definitely caused issues when all parts were recorded and I was starting to mix. While things didn't really sound distorted, it was always a struggle to get things fit come mixing time. Things have improved considerably since I have started to take it easy when tracking.
My recording chain (when dealing with external devices) is extremely simple, a couple of synths, and in some rare occasions a mic (SM7B). In fact, about 80% of the time, the only thing that ends up inside the DAW from the ouside world is
my Kurzweil K2600XS, which does have rather hot analog outputs (+21dBu Max on separate outputs, using balanced cables, and +27dBu Max on the Mix Outputs, again when using balanced cables). As long as I ensure that the gain staging is setup so that I don't digitally clip the signal inside the K2600, the analog outputs simply don't overload and the signal quality does not change even when pushing close to it's limits.
The second component is my Aardvark Pro Q-10. While it is a pretty decent sounding interface, it is also somewhat noisy, with a self noise floor of around -72dB or so, which is certainly rather high for 24bit recording.
That's about it for the background.
Before, I used to record so that I'd pretty much hit -1dbFS, and like I said, mixing was always difficult. I then started experimenting with lower recording levels, however, recording around -18dBFS (peaking) would cause noise buildup from the various tracks, so that was also an issue. The Q-10 allows me to lower the preamp level to -8dB (from unity gain), and when recording from Kurzweil with this setting I peak around -6dB or so (sometimes lower maybe down to -10dBFS), and that seems to give me the best overall balance.
So, from my experience, with the above equipment, there was certainly an issue when tracking close to 0dBFS.
Glen, a couple of questions regarding your post that I need some clarification on.
1kHz test tone. I can easily generate a 1kHz sine from the K2600. Will this work or do I need a specific test equipment for generating this?
I also have a multimeter, but I am not sure where I'd be measuring the voltages. Are you suggesting I simply check the voltages coming out of the Audio Outs of my Kurzweil (for example) while having it play a 1kHz sine wave and calibrate it's output so I read 1.23V and then connect that output to the audio in of my Aardvark Q-10 and adjust it's levels so that I read -18dBFS on the meters? I am somewhat confused about this process so if you don't mind dumbing down the process for me I'd appreciate.