2. Frequency Response Flashcards
What is a normalized frequency plot?
When a correction is made to the output plot due to inconsistencies in input level, or when the input level is intentionally varied to make it constant at all frequencies
What is frequency response?
A usable range of signal frequencies that will be passed from input to output
Only applies to signal processing devices and transducers
Tolerance
The max deviation in output level expected over stated range if input level is constant (+/- dB)
What does the frequency response plot of power amps or line amps look like?
Flat frequency response.
The limits are taken where the output is 3 dB below reference (20Hz- 30K, +0, -3dB)
Or states deviation within audible range when response greatly exceeds human hearing (20Hz-20k, +0, -1dB)
Octave, 1/3rd octave frequency response measurements
Octave interval is wider at high frequencies because of 2:1 ratio and correlate with human hearing so are widely used with loudspeakers
Divide linear scale into equal increments, As opposed to logarithmic scale like other plots
Pink noise is used for excitation signal
Narrow peaks and dips may be missed
Pink noise
Equal energy per octave
Rolls off at higher frequencies; less energy at the higher frequencies but more frequencies packed into the higher octaves (2:1) so when added up, each octave will be equivalent in energy
Average band energy will be measured separately
An audio cable comprises of
1 or 2 signal conductors (audio signal)
Shielding conductor: connected to electrical ground point, catch static/ radio interference shunting them to the ground
What can the capacitance and resistance of a cable act as?
A low pass filter, cutting off high frequencies and dulling sound which is proportional to the length of the cable
Mostly dependent on output impedance
What may attribute to the roll off at the frequency extremes of a power amp?
Subsonic filter pole: rejects ultra lows that could be damaging to a loudspeaker, or that could produce undesirable distortion
TIM (transient inter modulation distortion) filter: a high frequency roll off to minimize TIM and prevent tweeter damage
Why is the frequency response of a digital delay or digital signal processor different than most processors?
They use very steep input and output low pass filters (antialiasing and reconstruction filters) to avoid problems associated with digital signal processing
Significant roll off above the cutoff frequency of device up to 150 dB per octave
What are some general frequency response specs of microphones?
May have presence peaks from 3-6dB at 2-5k for crispness/ intelligibility
Condensers: peak from 8-10k because of diaphragm resonance leading to a slightly brittle/ bright quality
Ribbon: Presence peak and low frequency rise around 200Hz (great for voice)
Dynamic: falls off above 10k and below 100Hz
What can be expected of the frequency response of a loudspeaker?
Subject to great variation, often 10dB or more because their transducers have to handle large amounts of power and produce high sound pressures, so they must allow for durability
A good loudspeaker will have a tolerance of +/-4
General full range loudspeaker specs
Response from 100Hz to 10k/15k, should be at least 300Hz to 3.5k for voice
Directional
