Audio Engineering

Measurement 41

and 1/1000  0.001. Note that any E 2 and R 2 that result in a power of 0.001 W may be
used. We can then write:

Level (in dBm)

E

R

 10

0 001

1

2

1

log

.

(2.15)

a n d

ER

R

E

dBm

dBm

1110

1

2

10

0 001 10

0 001





.

.

⎛

⎝

⎜⎜

⎜⎜

⎞

⎠

⎟⎟

⎟⎟

⎟

⎛

⎝

⎜⎜

⎜⎜

⎞

⎠

⎟⎟

(^10) ⎟⎟⎟
⎟

.

(2.16)

See Figure 2.3.

For all of the values in Table 2.2 the only thing known is the voltage. The indication is
not a level. The apparent level can only be true across the actual reference impedance.
Finally, the presence or absence of an attenuator or other sensitivity control is not known.
See Section 2.20 for an explanation of VU.

RS

RS

RL

RIN

ES EIN

EL

(a) Power across a load in dBm

(b) Available input power in dBm

Figure 2.3 : Power in dB across a load versus available input power.