Audio Signal Level Monitoring Flashcards
Steps to Checking Signal Levels (5)
- Verify signals at all used mixer inputs
- Adjust gain levels wherever appropriate
- Turn on power amplifier, with volume level all the way down
- Slowly increase sound pressure to desired level
- Listen for distortion and correct as needed
Signal Monitoring
use of a visual display to monitor audio signal levels to ensure that the signal is not clipped or distorted
VU (Volume Unit) Meter Information (3)
- Designed to have ballistics (dynamic characteristics) that roughly approximate the human ear
- Works well with consistent signal levels
- Helps to prevent signal overload
VU (Volume Unit) Meter Common Use
Commonly used to monitor broadcast signals
PPM (Peak Program Meter) Information (4)
- Responds to signal level changes faster than a VU Meter
- Works well reading fast, transient sounds
- Shows instantaneous peak levels
- Helps prevent distortion in audio signals
PPM (Peak Program Meter) Common Use
Commonly found in audio mixers
Analog and Digital Signal Levels (2)
- With analog, running signal levels at around 0 dBu for line level signals is often preferred and there may be some occasions when the normal signal level exceeds 0 dBu.
- With digital however, the level must never exceed 0 dBFS. dBFS is the full scale (FS) of the digital signal. Exceeding 0 dBFS with a digital signal causes immediate distortion of the signal.
Interference and Noise (3)
- Signal processing circuitry and cables are continuously exposed to noise and interference
- This interference and noise degrades the quality of the audio signal and has the potential of introducing hum and buzz into our audio system
- Noise introduced into a digital signal can corrupt the data
Balanced and Unbalanced Circuits
One way to reduce the noise in a circuit or cable is to use a balanced electrical design
Balanced Circuit Definition
a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground
Unbalanced Circuit Definition (3)
- a two-conductor circuit in which one conductor carries the signal and the other conductor carries the return
- The return conductor is usually the cable shield and is a low impedance connection as it is connected to the signal ground and possibly also earth ground
- The impedance of the signal circuitry is quite different than the return circuitry, hence the impedance of the two conductors are quite different; the impedances are unbalanced with respect to one another
Balanced Circuit Description (5)
- In a balanced design, the impedance of high side of the signal circuit is equal to lowside of the signal circuit ground.
- The design of balanced circuits offers a defense mechanism against noise.
- This defense mechanism removes the noise, or most of it, leaving only the intended signal.
- As a rule, you should use balanced components whenever you can. The cabling used with balanced circuitry requires two signal conductors.
- In audio, the two signal conductors are surrounded by a shield.
Unbalanced Circuits Description (4)
- In an unbalanced circuit design, the equipment outputs an unbalanced signal to the cable that is connected to an unbalanced input.
- As with a balanced circuit, the cable picks up noise from surrounding sources.
- However, with an unbalanced circuit design, there are no noise defense mechanisms, except for the shield. So if noise gets onto the signal conductor there is no mechanism to remove it.
- Additionally, if undesired noise currents are flowing on the shield in an unbalanced circuit it actually becomes part of the problem and not one of the solutions.
Circuits and Noise (3)
- The longer the cable run, the more the cabling is subjected to noise
- Balanced circuits are less prone to suffer from noise pickup than unbalanced circuits
- Unbalanced lines are extremely limited in the distance they can cover
Feedback
unwanted noise caused by the loop of an audio system’s output back to its input.
