LeanneSP

I have been transcribing a series interviews recorded as m4a files. I have completed 7 with no problems and having loaded number 8 cannot hear any sound whatsoever. I have loaded the 9th file and that one is also silent. My foot pedal is working, the recording is moving on, but there is no sound and nothing happening in the db bar in the bottom left corner of the screen. I have been unable to find any guidance either on the software or anywhere online and am utterly perplexed. Have looked at 'options' and so on, fiddled with various volume settings but no joy. This is work for a client and they require a fast turnaround so I'm getting desperate now and would be most grateful if anyone can tell me what's going on!! Many thanks!