Exam 2: Amplifiers & Compressors Flashcards
pre-amp
FET
final amplifier
output amplifier
what is field effect transistor
pre-amp
takes the analog electric signal and adds amplitude to make it bigger and easier to go through the rest of the components
what is transistor based amplifiers
there are multiple throughout the ha
past pre amp but before vc
adds gain to input signal in order to increase the amplitude of the electrical signal
what is output amplifier
additional gain added at output level for max output to arrive to the receiver that will be transitioned to the acoustic signal
What is an input/output curve (I/O)
chart showing intensity of input compared to output at the TM
I/O axis representation
x axis is db SPL representing the input signal
y axis is db SPL representing output arriving to ™
what is linear amplification
adds same gain to all inputs
uses 1:1 compression ratio
linear
what is meant by 1:1 compression ratio
for every 1 spl increase in input, 1 spl increase in output occurs until max output is reached
Cochlear damage causes __________ perception
abnormal loudness growth
does linear amplification restore normal loudness growth
no
takes all sounds and adds the same gain
why doesn’t linear restore abnormal loudness growth
because it applies same gain at all inputs so they have some signals underamplified and other signals that are overamplified
what is a compressor/compression
level detector
used to fit amplified signals into reduced dynamic range
when an input gets loud compressor automatically kicks in and compresses the signal adding less gain to it
provides nonlinear amplification
aka automatic gain control
compression/compressor
provides nonlinear amplification
compressor/compression
what is compression ratio
determines how much gain is added to the input signal
refers to that for every increase of x dB how much output will you get
what controls affect compression
Threshold kneepoint (TK)
Attack time
Release time
Compression ratio
when level detectors & compressor are activated at pre amplifier before volume control
AGCI-I
when level detector is associated with output compressor, after volume control
AGC-0
what is threshold kneepoint
changing from 1 compression ratio to another
point at which slope of I/O fxn changes
what is a high TK
> /= 85 dB SPL
what is a high tk used for
to limit ha output so it doesn’t exceed individuals LDL
what is a low tk
</= 50dB SPL
what is a low tk used for
to improve audibility of softer speech components
what is attack time
time that it takes a compressor to turn on when the input is loud enough
hwo long it takes compressor to kick in full gain reduction after exceeding threshold
overshoot
fast attack time
sudden loud sounds
fast at
speech signals
slow attack time
what is overshoot
period of over amplification
output signal overshoots targeted SPL
what is release time
time it takes for compressor to deactivate when level falls below TK
undershoot
release time
what is undershoot
output signal undershoots targeted SPL
period of under amplification
what are the pros of fast compression (fast at/rt)
better for sudden loud sounds
soft sounds remain audible following RT
consonants stay audible after loud vowel sounds following RT
what are cons of fast compression (fast at/rt)
speech envope changes so what you are used to hearing and understanding is altered and the brain know longer recognizes the signal that is stored
uses more working memory because auditory memory has changed
what do PT’s with low cognitive abilities benefit from
slower at’s
what population wears HA’s? what population can experience cognitive decline?
geriatrics
a lot prefer slow acting because it keeps spectral env and easier to match the signal to their auditory memory
pros of slow compression (slow at/rt)
keeps original spectral envelope for easier processing in those with poor working memory or severe HL
promotes naturalness of sound
listening effort decreases
ILD preserved bw ears
cons of slow compression
sudden loud sound attenuates output signal during conversation making speech briefly inaudible
best suited for sudden loud sounds to maintain comfort, and avoid auditory damage
fast attack
best for conversational speech to maintain the shape of the spectral envelope
slow attack
depends on the intensity & duration of an activating signals.
release time
brief, intense sounds (such as a door slamming)
fast release time because uncompresses quick to maintain speech signals following
longer intense sounds (such as a raised voice)
longer release time because it maintains a comfy output level during brief gaps of silence
yelling (at/rt)
fast attack, slow release
what is a compression ratio
how much compression to apply
how much gain to add to the input signal
what is harmonic distortion
frequency components that are added to a HA output that wasn’t in the input signal
what results in an amplified signal results in a distorted output signal
aggressive clipping
what is a bill circuit
bass increase at low level circuit
in noisy environments >50dB LF output is reduced to limit loudness of noise to improve understanding in noise
what does cutting LF gain sound like
tinny and harsh
what are till circuits
HF gain increases when overall input is quiet to help audibility of soft sounds in QUIET
what is a kamp circuit
most common till still used today
musicians love this because it doesn’t change shape of the sine wave & lets loud sounds through with no distortion and makes signal more clear
as input level increases the responses flatten
what are the types of compression
expansion, WDRC, OLC
whenever there is a change
TK
what is the purpose of output limiting compression
compression is applied to loud output signals in order to protect the ear from over amplified sounds
what are the benefits of OLC
reduces but doesn’t limit distortion
maintains output intensity below LDL
stops the risk of NIHL
Only peak clipping result in distortion and loss of acoustic detail, but OLC distortion is less noticeable
false, they both result in distortion
Helped loudness tolerance in linear devices but didn’t restore audibility of soft input signals or normal loudness perception
OLC
what is maximum power output (MPO)
devices loudest ouput it can produce no matter the input level
what is peak clipping
happens when signal exceeds threshold
form of compression
stops output increase aggressively and clips the amplitude once the signal’s intensity reaches the circuit max
what is WDRC theory
soft input needs more gain than intense sounds
frequency response should change with varying input levels
how does WDRC restore loudness growth function of HI PT
the low CR in WDRC shapes sound into dynamic range adding gain at low TK to improve soft sound audibility
it adds more gain to soft sounds and less gain to loud sounds allowing for more access to sound before output reaches LDL
why does linear amplification not restore loudness growth function
because it adds the same gain for every input resulting in under amplified and over amplified sounds
Explain how raising/lowering a TK input level alters the output of signals at or below the TK.
shifting TK lower increases output for soft signals at or below TK
raising TK decreases output for soft signals
as TK is lowered output signals increase
WDRC improves audibility of soft consonant sounds
OLC applies increased CR to loud input signals earlier for increased comfort
as TK is raised output signals decrease
reduces audbility of soft LF background noise
increases device MPO when PT can tolerate greater output of loud input signals to improve clarity
if a PT needs more clarity of consonant sounds
shift tk down
Bob can actually hear and perceive soft sounds as being soft; he likes them and wants to hear all of them. They make sense to him and enrich his hearing experience. How would you shift TK
lower it
Sam has difficulties coping with all the soft sounds in his environment, which he tends to describe as “noise” rather than sound. He has difficulties making sense of these soft sounds.
how would you shift TK
raise tk
as input increases amount of gain applied is reduced
compression
as input increases amount of gain applied is rapidly increasing
expansion
let’s HA sound silent when in quiet environments
expansion
Differentiate AGC-o from AGC-i based on their location, function, and associated types of compression
o- after vc, at the output level, manages loud sounds and compresses them before going into the PT’s ear, OLC >/= 80 dB SPL
i - before VC, manages incoming sound, compresses at pre-amplifer when input is louder than TK
b/w 20-50 dB SPL (WDRC)
when do we use expansion
when someone complains about soft sounds they find annoying and do not need to hear
location, TK, CR of expansion
0-20 dB input
really low CR; lower than linear (1:1)
</= 0.9:1
when is WDRC used
use this when soft sounds need to get louder and need to expand dynamic range
input compression, before the volume control
activates at the pre-amplifier, when input is louder than low TK
aka AGC-i
location, TK, CR, AT/RT of WDRC
before vc/preamplifier
TK bw 20-50 dB
CR bw 1.1-4.1 (LOW cr; almost linear)
slow AT/RT
how does WDRC work
a lot of gain is added to soft signals for audibility, minimal gain is added to moderate sounds and even less gain is added to loud sounds
why do we want slow at/rt in wdrc
slow at: preserves temporal envelope of speech signal
slow rt: reduces inaudibility time of soft consonant sounds after compression release
restores loudness perception
WDRC
when do we need OLC
needed for loud sounds to protect the ear
AGC-o
limits MPO so HA doesn’t exceed LDL
location, tk, at/rt/ cr of OLC
engages AFTER VC
tk: >/= 80dB SPL
high cr: >/= 5:1
AT: fast to protect ear from loud sounds
RT variable (fast = sudden noises, slow = sustained loud noises)
which mic has the best DI
hypercartiod
what is DI of hypercartiod
6.0 dB SNR
what is DI of supercartiod
5.7 dB SNR
what is DI of cartiod
4.8 dB SNR
DI of omnidirectional
0 dB SNR
what have we learned so far
Sound comes into mic (either in or out of phase; in goes on out is nulled), MEMS or ECM mic transduces acoustic signal by compressing and decompressing the diaphragm and the backplate creating the + and - analog electrical signal
Went from carbon balls, to piezoelectric now to MEMS or ECM
MEMS is better - used for PT who needs durable, rigorous HA; used for construction worker who is outside and sweats all day or someone who lives in humid environment like florida or new orleans, or even someone who leaves their HA in their car MCM - less durable & more susceptible to heat & humidity; grandma that lives in assisted living
NOW, sound leaves mic and goes through a bunch of circuits that either compress or amplify the signal
Signal is either amplified (transistor) or compressed (resistor) and is either routed to AGC-i or AGC-o
Either amp or level detector determines if sound needs to be compressed (detecting how loud it is)
AGC - i: electric signal comes in and either goes on or is compressed
AGC-o: goes through all DSP and out on other side of VC and either is amplified or compressed by OLC
Then sound goes to the receiver to be transduced back to an analog acoustic signal
what is slow acting compression good for
good for those with lower cognitive capacity because temporal envelope is not compressed and looks more like what our brain stored of the sounds; while someone speaks, amp of temporal envelope shape is closer to auditory memory of signal for longer periods of time
what is fast acting compression good for
gets compressed, work harder to match sound is sort of a memory to understand and causes more listening effort resulting; doesn’t take a lot of volume for it to compress & envelope doesn’t look like memory of it working harder to understand what was said
fast AT slow RT
Loud sustained sound
do not want the pumping of compressors turning on and off
fast AT/RT
loud sudden sound
fast release
abrupt vowel sound like laughing in the middle of talking
what is a frequency shaping band
frequency response is a series of VC called bands/handles
VC’s that separate individual frequency ranges, doesn’t change CR, adds gain equally for soft, moderate and loud input signals
ROWS
what is compression shaping channels
COLUMNS
shape compression characteristics into individuals dynamic range
what settings are adjusted in compression shaping channels
expansion threshold tk wdrc cr olc and they all vary by frequency
what do contemporary devices have
multiple TK’s with different CR within a frequency range
how can you maximize speech intelliginility in contemporary HA’s
multichannel wdrc
what does multichannel wdrc do
vary expansion - reduces low level noise present in any channel
vary tk - enahcne speech signal present in any channel
vary CR - optimize dynamic range in any channel
vary MPO - for tolerance within different frequency ranges
what is curvilinear compression
CR increases as input increases creating the curvilinear shape
