The PJB BigHead is not big at all. In fact it is barely larger than an iPhone. The "Big" is about the sound. It functions first as an awesome bass headphone amplifier with 2 band EQ ( +/- 18db @ 60 Hz and +/- 18dB @ 5KHz) set for optimization of all kinds of bass instruments.
Unlike consumer electronic MP3 players and smart phones that have very small power output of around 20 milli-watt to drive headphones, the BigHead has more than 10 times the power. This contributes to a far more exhilarating listening experience with increased resolution and dynamics. Even if you are just listening to music, the BigHead will be a great improvement to your regular headphones, adding more listening pleasure.
A more important function of the BigHead is being a recording tool both in digital and analog. As an Analog Digital Converter, it has the finest BURR BROWN digital components. The USB out is 48KHz 16Bit digital conversion. In other words, recording your bass onto Pro Tools will give you exactly what you wish for and absolutely nothing else.
Maybe you need an analog pre amp. The Big Head can do that too. It will provide up to 12dB of gain and better than 96dB signal to noise ratio. Just use the headphone out jack to feed an amp or mixer. It has an internal lithium-ion rechargeable battery that is fed by its USB jack, so any computer or appropriate cell phone charger can charge it in less than 3 hours, but it can play for up to 8 hours.