Signal Processing Flashcards
Three Types of Basic Signal Processing Equipment
Frequency Domain
Dynamic Processors
Time Based (Enhancers)
Cut-Off Frequency
Point where signal has dropped -3dB
Slope Order Rate
Slope is at a constant rate
✤ First order: 6 dB/8va
✤ Second order: 12 dB/8va
✤ Third order: 18 dB/8va
Notch Filters
✤ Very narrow band - normally to attenuate problems
✤ 60 Hz hum
✤ Usually covers the 2nd harmonic (octave) as well
Shelving Equalizer
The response rises or falls then levels out
Identified by the Turnover Frequency
This is the point levels out
3 dB before the maximum amount of boost or attenuation
Peaking Equalization
Stated by it’s center frequency
✤ Bandwidth
✤ Expressed as Q (quality factor)
Parametric Equalization
Frequency selection is variable over a wide band ✤ Variable amplitude ✤ Variable Q ✤ Sometimes switch selectable
Graphic Equalizers
✤ Gives a Graphic display ✤ Each band is peaking type EQ ✤ Bandwidth is not adjustable ✤ Narrow bandwidth Based on International Standards Organization Octaves to 1/6 octaves
Passive EQ
does not amplify
Passive elements attenuate the signal around the audio band to be boosted
Phase shift due to the use of inductors and capacitors
Fixed gain raised the entire audio band
Active EQ
Amplifier
Gain Riding
Manual Compression
Electronic Gain Riding
An electronic circuit whose gain varies automatically as a function of the input signal
Compressor
A variable gain amplifer in which the dynamic range of the output signal is less than that of the applied input signal
CompressionAttack time
The time it takes for compression to begin
Compression Release Time
The time it takes the out put to restore itself
to unity gain
Breathing or Pumping
A great fluctuation around the threshold will cause a rise and fall of background noise
A fast release time can be a problem with
pumping and breathing
Limiter
A compressor with a ratio of 8:1 or greater
Expanders
A variable gain amplifer in which the dynamic range of the output signal is greater than that of the applied input signal
Noise Gate
An expander whose parameters are set to sharply attenuate an input channel
Key Input
Allows an external source to trigger the output of an compressor/ limiter or expander/gate through a side chain
De-Esser
Am equalizer is inserted into the CV side chain of a compressor
Soundfield
A complex combination of direct and reflected energy that exists in a living environment
✤ Time delay
Direct to reflected energy ratio
✤ Sound level (placement)
✤ Frequency response
✤ Visual cuesDirect sound
The sound wave travels in a straight path to the listener
✤ no way to simulate this
Echo
✤ A single repetition that arrives some time after the direct sound
✤ Delay is the time it takes for a discrete echo
Decay
The attenuation of sound field over time
Early Reflections
✤ A few closely spaced echoes that arrive shortly after the direct sound
Reverberation
✤ As time goes on more and more echoes arrive
✤ The echoes are so close it is impossible to distinguish them from one another
Reverberation Time
✤ The time it takes for the reverberation to decrease 60 dB
Time Delay systems
✤ A system that can store a signal and reproduce it after a suitable time
Haas Effect (1949)
✤ 0 - 10 ms: Image shift (The delayed speaker will have to be raised
about 10 dB)
✤ 10 - 30 ms: Sound from the primary source, sense the delay but not
the direction
✤ 30 - 50 ms: Become aware of the delay
✤ 50 ms and up: Primary source and discrete echo
✤ These are all approximate and vary with the sound and application
Tape Delay
t sec = d in/s in/sec
Analog Shift Register (Bucket Brigade)
✤ Transfers a charge from one capacitor (register) to the next ✤ Problems ✤ Residual loss ✤ transfer loss ✤ thermal semi-conductor charge loss
Spring Reverberation
Developed by the Hammond Organ Co.
Plate Reverberation
✤ Dr. Walter Kuhl (1957) Institute of Broadcasting Technology, Hamburg ✤ Excite a steel plate with a transducer ✤ 1/64” thick and 6’ X 3’ ✤ Two pickups ✤ 3:1 rule
Digital Reverberation
Simulates all aspects in the digital domain
Pitch Change
✤ Signal is sampled at one rate and then played back at another
rate
✤ To keep the original length …
✤ … samples must be removed to lower the pitch
✤ … samples need to be added to raise the pitch
Flanging
✤ With a delayed replica some frequencies are reinforced while others are canceled as a result of time shifts.
✤ Time shift varies resulting in a sweep up and down the frequency spectrum
Phasing
An attempt to duplicate the effect of flanging using a phase shift network
Move a notch filter with a high ‘Q’
Depth= how for the center frequency, oves
Speed= how quick the movement is
Phasing is not as apparent as flanging
Aural Exciters
Excites even order harmonics
Newer units allow control of both even and odd harmonics
Time Compression/Expansion
✤ Lengthens or shortens the duration of a signal with no change in pitch
