“I used my camera to achieve this” makes no sense at all. You capture video and audio via firewire interface. An audio signal from a cassette player, is line level. If you hope to capture that audio correctly, it must be connected to the proper input level. (line level in the case of a cassette player). I truly hope this makes sense to you? Do you not have a line level input in your audio card? If not, you will need the attenuator. This is all, providing you want to add sound to your already captured clips? Either way, once you have the correct connections, test the audio quality in Vegas using the record button, on an audio track. You should get pristine sound from an audio cassette deck in this manner, providing the source sounds are good, to begin with.