No values without a bit of history…
Back in the early days of broadcast, both 10.0 and 12.5 mW into a 500 ohm line were used as common reference levels that indicated 0VU. In May of 1939, we adopted the current standard of 1mW into a 600 ohm line.
Now you would think that this was driven by the recording industry.
NO No no! It was driven by the telephone company’s standard of limiting the signal level of transmission for a minimum of crosstalk and still provide a satisfactory signal to noise ratio in copper phone lines.
It just so happens that the audio industry then adapted that standard and it has been with us in the recording world ever since.
So our first standard reference level for analog gear is 1mW into a 600 ohm line and is denoted as a dBm. Or more completely as 0VU dBm.
Now I ask you, is your meter set to read dBm?
Next week we will talk about the dBv and others.