How about this Sony patent that references Norris patent:

Recording and/or reproducing apparatus and recording apparatus

A recording and/or reproducing apparatus includes a microphone, a semiconductor memory, an operating section and a controller. An output signal from the microphone is written in the semiconductor memory and the written signals are read out from the semiconductor memory. The operating section performs input processing for writing a digital signal outputted by an analog/digital converter, for reading out the digital signal stored in the semiconductor memory and for erasing the digital signal stored in the semiconductor memory. The control section controls the writing of the microphone output signal in the semiconductor memory based on an input from the operating section and the readout of the digital signal stored in the semiconductor memory. The control section operates so that, when the signals written in the storage section are read out from it, an input for erasure is entered by the operating section, and the signal being read out from the storage section is erased when, after reading out the signal from the storage section for a pre-set period, an input for erasure is again entered from the operating section.

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=6,289,253.PN.&OS=PN/6,289,253&RS=PN/6,289,253