No I don't know what it is, but I will take a guess.

Since we are talking Hi-Fi I assume a FS signal level of -10dBv. dBv reference is 1V RMS. So it is quite likely I am talking about -0.5dBv relative to whatever the signal level was at the time.

I have to say though it has been 3 years since I last tried to remember all the reference's for dB measurements so I may be a bit rusty! It is dBu with a 0.775V reference isn't it? Not dBv..    lol! I'm going to look silly now ain't I.