It would record silence. It doesn’t use more RAM the more it records, however. It is allotted the amount of RAM it needs when it is created, determined by the first argument. For most purposes, any large amount of samples you put in there will be more than musically necessary and still a laughably small amount of RAM. If you are using a machine which is young enough to run Max/MSP, you will have enough RAM. We installed Pure Data on some older machines at our theater to route MIDI, and the problems they have when processing Audio result from other bottlenecks than the RAM.