The 664 Six-Channel portable production mixer with integrated recorder from Sound Devices has an unprecedented amount of functionality from a unit that can be battery operated. It starts with a low-noise, transformerless preamplifier section, continues to an intuitive mixing surface, adds a host of digitally-controlled routing features, allows room for analog inserts and aux busses, and finally terminates with versatile, plentiful output connectivity. The 664 can be configured to record digital audio to CompactFlash and/or an SD Card from any point in that signal flow. The Sound Devices 664 has an input board that features six balanced XLR connections. Within the firmware, they can be selected to accept microphone or line level signals. Additionally, inputs 1 and 6 can configured to accept AES digital signals. Each channel has a direct output on an independent TA3 connector. There is also an input for a slate microphone, if you don't wish to use the 664's internal slate mic. Two headphone outputs are also provided. The physical mixing surface of the 664 has the basic features you'd expect, such as trim pots, panning and level knobs. But it also has more advanced features, like sweepable high-pass filters and pre-fader listen switches on each channel.