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Review #2
*What does Unity Gain mean? - Always means Output = Input in every gain stage
*We have 6 measurements for determining the amplitude capabilities of audio equipment. Identify each part with the correct letter on the Amplitude graph:
A - Noise Floor B - Maximum Operating Level C - Standard Operating Level D - Signal to Noise Ratio E - Headroom F - Dynamic Range
*Impedance Bridging means "Input impedance is always at least 10 times higher than Output’s"
*Balanced lines have 2 signal leads and a shield *Unbalanced lines have 1 signal lead and a shield
*The 3 signal levels of pro-Audio are: 1. Mic (50 mV typical) 2. Line (1.23V = 0 dBVu = +4dBv standard) 3. Speaker (10V typical) level
*Standard Operating Level (SOL) is: +4 dBv = 0 dBVu = 1.23 volts (Pro Level) -10 dBv = 0.775 volts (Consumer Level)
*Overall Current for Parallel Circuit: I total = I1 + I2 + I3 +…
1. Mic Level: 50 mV (typical)
2. Line Level: - Pro Line Level: 1.23V = 0 dBVu = +4 dBv - Consumer Level: 0.775V = -10 dBv
3. Speaker Level: 10V (typical)
- MOL (Maximum Operating Level): +20dB / 24 dBv - ROL (Reference Operating Level/SOL): 0 Vu = 0 dBVu = +4 dBu = 1.23V
- Only read and show average of signal. Not the actual level of signal. Completely ignore peak
- Read absolute level (not average)
*Bel - A Bel is defined as the logarithm of an electrical, acoustic, or other power ratio. - Bel = log (P1 ÷ P2) - P1, P2 —> two power values (watts)
*Decibel - The decibel is actual 1/10 of a Bel - dB = 10log(P1/P2) - The dB always describe ‘a ratio of two power’ ==> thus has always reference
*dBm - Express ‘electrical power level’ - Always reference to 1 milli watts - 0 dBm=1 milli watt - In the case of only 600 Ω circuits, 0 dBm = 1 milli watts = 0.775 volts
*dBu - is more appropriate term for expressing output / input voltage - 0 dBu = 0.775 volts (always)
*dBv - a “0.775 volt” zero reference - if one assume a ‘600 ohm’ circuit: 0 dBv = 0.775 volts +4 dBv = 1.23 volts = 0 dBVu
*dBV - a 1 volt zero reference regardless of circuit impedance - So, 0 dBV = 1 volt rms (root mean square)
E = I x R I = E ÷ R R = E ÷ I (P = I x E)
*Resistance in Series circuit R = R1 + R2 + R3 + etc. = R total
*Resistance in Parallel circuit R = 1/R1 + 1/R2 + 1/R3 + etc. = 1/R total
*Power formulas P = I x E P = E^2 / R P = I^2 / R
*Wavelength (in air) λ = velocity (1130 ft /sec) / frequency
*dB Watts - dB watts = 10log(P1 ÷ P2) (because Watts means power)
So, 100 watt power amplifier is: 10 log(100 ÷ 1) = 10 x Log 10^2 = 20 dB (∵ 0 dBw = 1 watt)
*dBu - dBu is a more appropriate term for expressing output or input voltage than dBm - 0 dBu = 0.775 volts
*dBv - If one assume a ‘600 ohm’ circuit: 0 dBv = 0.775 volts
- dB is used to describe sound pressure levels - Another term for voltage is electromotive force - The force of air pressing against the resistance of an eardrum is analogous to the force of a battery pushing electrons against the resistance in circuits - Thus, dB SPL = 20log(P1/P0), where P1, P0 are sound pressures, in dynes (unit of force in the cm) per square centimeter
*20log(E1/E0) - The dB can be used to express voltage ratios - Power is proportional to the square of the voltage
*Voltage drop for series resistance: (I x R) + (I x R) + (I x R) + etc = Etotal
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