Thanks for the replies.
So, the mono mix sounds like a low bitrate mp3 because it was source from an mp3? 😃 Thanks for the link, I’ll get it asap.
…
No, I was given a lossless WAV file which had already had Noise Reduction applied, and the “Raw” MP3. I don’t believe for a second that it was captured as an MP3 at 128 KB/s. I’m sure it was captured as PCM, and if I had asked for it I could have used that instead, but all I would have done would be apply a noise reduction using Adobe Audition by sampling the hiss, which probably would have been worse, so I just went with what they gave me.