Signal Processing Flashcards by Timothy Mattaliano

Three Types of Basic Signal Processing Equipment

Frequency Domain
Dynamic Processors
Time Based (Enhancers)

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Cut-Off Frequency

Point where signal has dropped -3dB

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Slope Order Rate

Slope is at a constant rate
✤ First order: 6 dB/8va
✤ Second order: 12 dB/8va
✤ Third order: 18 dB/8va

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Notch Filters

✤ Very narrow band - normally to attenuate problems
✤ 60 Hz hum
✤ Usually covers the 2nd harmonic (octave) as well

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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

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Peaking Equalization

Stated by it’s center frequency
✤ Bandwidth
✤ Expressed as Q (quality factor)

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Parametric Equalization

Frequency selection is variable
over a wide band
✤ Variable amplitude
✤ Variable Q
✤ Sometimes switch selectable

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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

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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

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Active EQ

Amplifier

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Gain Riding

Manual Compression

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Electronic Gain Riding

An electronic circuit whose gain varies automatically as a function of the input signal

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Compressor

A variable gain amplifer in which the dynamic range of the output signal is less than that of the applied input signal

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CompressionAttack time

The time it takes for compression to begin

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Compression Release Time

The time it takes the out put to restore itself

to unity gain

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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

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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 cues

Direct 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