[tomhazledine]

That's a great point. The piece was written from a very web-centric point of view. Even though I used analogue mixing desks as my jumping off point, I only really looked at decibels in a digital context.

In fact, all the digital VU meters I've looked at do account for positive values, so I definitely shouldn't have breezed over that aspect so quickly.

[wrigby]

This varies from product to product; for example, meters in Pro Tools are labeled directly in DBFS[1]. So are Yamaha digital mixers (at least the LS9 and M7 - not sure about the newer ones).

On the other hand, the Allen & Heath GLD has its meters labeled differently, and I'm not quite sure what they're referenced to (they go up to +12). This can be a bit frustrating, since I never know how close I am to digital clipping, but in practice I aim to get everything around 0 dB on the meters and I have at least 12 dB of headroom.

Wikipedia has a neat list[2] of different analog reference levels for 0 dBFS.

1: Pro Tools metering - http://i.imgur.com/YcUBR6H.png

2: https://en.wikipedia.org/wiki/DBFS#Analog_levels