signal level matching

Question 1

give 3 field quantities

Answer 1

voltage
current
pressure

Question 2

give 2 power quantities

Answer 2

intensity
power

Question 3

give the relationship between power and field quantities

Answer 3

field quantities² ∝ power quantities

Question 4

give the dB equation of power and field quantities

Answer 4

power - dB = 10 log (R2/R1)

field - dB = 20 log (R2/R1)

Question 5

what does 0dBu or 0dBv mean?

Answer 5

voltage of 0.775 V in 600 ohm impedance

Question 6

what does 0dBV mean?

Answer 6

voltage of 1V in a 600 ohm impedance

Question 7

what is the nominal operating level?

Answer 7

equipment operating at optimum voltage, when the optimum voltage is input into the device

too much V = distortion
not enough V = noise can occur

Question 8

give the range of voltage produced by mics and how does a preamp help mics?

Answer 8

1mV to 100mV

a preamp will amplify the voltage to a line level for onward processing

Question 9

define headroom

Answer 9

headroom is the unused capacity to reach a signal standard

Question 10

if we wish to amplify a mic signal from 10mV (0.01V) to about 1V, what is the dB in gain?

Answer 10

delta dB = 20 log (final dB/start dB)

dB = 20 log (1/0.01)
dB = 20 log(100)
dB = 40

Question 11

what is dBFS?
what is 0 dBFS in dBu?

Answer 11

dB full-scale is a digital standard
0 dBFS (-18dBu) is always the max, going down using negative numbers
the bottom of the scale is -6n dBFS where n is the number of bits.
for 16 bit, the scale goes to -96 dBFS

Question 12

what does +4dBu mean?
what does -10dBV mean?

Answer 12

+4dBu is the standard for professional equipment, it means a voltage of 1.228 V

-10dBV is the standard for commercial equipment, it means a voltage of 0.316 V

Question 13

what is dBVU?
what is 0dBVU in dBu?

Answer 13

dB volume unit - reads the average level of a signal in 300ms segments which works well with speech patterns

0dBVU = +4dBu for sine wave input

different freqs affect the dBVU needle differently

Question 14

what is 0dBm?
0 dBm in dBu?

Answer 14

dBm is a power quantity, 1 mW of power into 600 ohms

+4dBm is a standard
0dBm = 0dBu = 0.775 V, only if impedance is 600 ohms

used in power amps and power supplies