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Figures for Chapter 6 Compression. Dillon (2001) Hearing Aids. Varieties of compression. High Level. Wide Dynamic Range. Low Level. Weak. Weak. Intense. Weak. Intense. Intense. Moderate. Moderate. Moderate. Input level.

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figures for chapter 6 compression

Figures for Chapter 6Compression

Dillon (2001)

Hearing Aids

slide2

Varieties of compression

High Level

Wide Dynamic Range

Low Level

Weak

Weak

Intense

Weak

Intense

Intense

Moderate

Moderate

Moderate

Input level

Figure 6.1 Three ways in which the dynamic range of signals can be reduced. In each case, the upper figure shows the spacing of different signal levels before amplification (the left end of the lines) and after amplification (the right end of the lines). The lower figure shows the same data, but as an input-output function.

Source: Dillon (2001): Hearing Aids

slide3

Compression waveforms

Output:

Pressure

Input:

Time

Figure 6.2 Waveforms that are input to a compressor and output from a compressor, showing the attack and release transitions that follow an increase and decrease, respectively, in signal level. The dotted line shows the envelope of the positive half of the signal.

Source: Dillon (2001): Hearing Aids

slide4

Ts

Linear

Slow

Ta= Tr = 10Ts

Medium

Ta = Tr = Ts

Fast

Ta = 0.1Ts

Tr = 0.3 Ts

Compressed envelopes

Figure 6.3 Envelopes for the output signal coming from a linear amplifier and compression amplifiers with different attack times (Ta), and release times (Tr) compared to the duration of each syllable (Ts) in the signal.

Source: Dillon (2001): Hearing Aids

slide5

Feedforward compression

Delay

Detector

Figure 6.4 A block diagram of a feedforward, look-ahead compression control circuit.

Source: Dillon (2001): Hearing Aids

slide6

I-O curve

and

gain-input curve

Figure 6.5 Upper: input-output diagram showing the definition of several static compression characteristics. Lower: the graph of gain versus input that corresponds to the I-O curve above it.

Source: Dillon (2001): Hearing Aids

slide7

Cuvilinear compression

Figure 6.6 Input-output characteristics corr-esponding to curvilinear compression(solid line) and a fixed compression ratio combined with compression limiting (dashed line).

Source: Dillon (2001): Hearing Aids

slide8

Output (dB SPL)

Vol max

100

90

80

70

Input (dB SPL)

60

50

Vol min

40

40

50

60

70

80

90

100

110

Vol max

F

100

Output (dB SPL)

90

80

70

Vol min

60

Output controlled compression

50

40

40

50

60

70

80

90

100

110

Input (dB SPL)

F

Input controlled compression

Figure 6.7 Input controlled compression and output controlled compression: their block diagrams and the I-O curves for each as the volume control is varied from maximum to minimum positions.

Source: Dillon (2001): Hearing Aids

slide9

Linear and compressed envelopes

Figure 6.8 (a) Envelope of the signal The yellow flower has a big bud put into the hearing aid at two levels. The thick curve shows the envelope for linear amplification and the thin red curve shows the envelope for a compressor with a 3:1 compression ratio, attack time of 20 ms, and release time of 200 ms. Part (b) shows the gain applied by the compressor. Part (c) shows the envelope for linear amplification and for compression when the attack and release times of the compressor were increased to 1000 and 2000 ms respectively. The corresponding gain is shown in part (d).

Source: Dillon (2001): Hearing Aids

slide10

Figure 6.9 Input-output curves for medium level compression, wide dynamic range compression, and linear amplification, all combined with either compression limiting or peak clipping of high level signals.

Source: Dillon (2001): Hearing Aids

slide11

Loudness

normalization

Figure 6.10 (a) Loudness growth curves for normal hearing people and a hearing impaired person with a 50 dB hearing loss. (b) Insertion gain needed for the impaired listener to receive a normal loudness sensation. (c) The corresponding I-O curve.

Source: Dillon (2001): Hearing Aids

slide12

(b)

+

(c)

50

Gain (dB)

90

0.1

0.2

0.5

1.0

2.0

5.0

Frequency (kHz)

Loudness

normalization

(TILL)

(a)

Figure 6.11 Block diagrams of (a) two-channel and (b) single channel processing schemes that can implement approximations of loudness normalisation, and (c) the resulting typical TILL gain-frequency response that increases in slope as the input level decreases from 90 to 50 dB SPL.

Source: Dillon (2001): Hearing Aids

slide13

Possible masking

Input Spectral

Level

(a)

Signal

Noise

(b)

Gain

Noise

(c)

Signal

Output Spectral

Level

1 kHz

Frequency

Noise reduction

Figure 6.12 (a) Spectrum of the signal and noise input to a noise reduction hearing aid. (b) Gain applied to the signal and noise. (c) Spectrum of the signal and noise at the hearing aid output.

Source: Dillon (2001): Hearing Aids

slide14

+

Noise reduction (BILL)

Figure 6.13 Block diagrams of two-channel and single-channel processing schemes that can implement simple noise reduction strategies, and the resulting BILL response that decreases in slope as the input level decreases from 90 to 50 dB SPL.

0.2

0.1

0.5

1.0

2.0

5.0

Frequency (kHz)

Source: Dillon (2001): Hearing Aids

slide15

Output levels

Output

range

Input

Range

Linear

Compression

Output level

70

Input level

Figure 6.14 Input-output functions for two different hearing aids adjusted to have the same output for a 70 dB SPL input signal.

Source: Dillon (2001): Hearing Aids

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