Wearable Speech Enhancement
Final Report
11/12/04
Team Members:
John Dimmick
Brandon Mikulis
Carl Audet
Coordinator:
Prof. Slack
Advisor:
Dr. Amuso
Sponsor:
Dr. Perlman
Project Overview: Patients with Parkinson’s disease often experience a wide array of
symptoms including speech impediment. A common Parkinson’s related speech
impairment is the loss of voice intensity. As a result they are difficult to understand in a
noisy environment. While this loss in voice intensity can leave the patient and those
people whom they come in contact frustrated over the inability to effectively
communicate, it may be possible to overcome this issue through the use of voice
amplification. The objective of this project is to create a device that amplifies the speech
of a Parkinson’s patient in a noisy environment to the point where it can be easily heard
and understood by those in the patient’s immediate vicinity.
Previous Attempts: It has been common practice to provide patients with small
microphones that can be attached to a collar or placed in close vicinity of their mouths.
In order for the patient to be heard by other people the microphone is connected to an
amplifier which drives a small speaker. Sadly, this arrangement has proved to be far
from the optimal solution and the problems associated with this method are listed below.
A. Background Noise – While amplifying the patient’s voice the amplifier also
amplifies ambient noise resulting in signal-to-noise problems. Therefore, a large
amount of background noise, combined with the weakened state of the subject’s
voice, makes the broadcasted speech very difficult to comprehend.
B. Acoustic Feedback – When the volume control is set to a comfortable listening
level the speaker often produces a high pitch squealing noise which renders the
device useless as a result of its close proximity to the microphone resulting in
acoustic feedback.
Wireless Transmission: A wireless link is required between the sensor located on the
individual and the movable speaker unit which is to be located in the person’s immediate
vicinity, possibly attached to a wheelchair. A transmitter capable of transmitting voice
quality data with a maximum frequency of no more than 2 kHz over a distance of 1 of 2
meters is required. The transmitter is to be limited in size and power because it would be
ideal to incorporate the transmitter into the same collar as the sensor. Three different
methods of wireless communication were examined.
A. IR: Infrared (IR) Transmission is used in a variety of wireless communications,
monitoring and control applications. IR Transmission is used to transmit digital
data over short to medium range distances. Transmitting IR data between two
devices is accomplished using a beam of IR light. Because infrared transmission
requires a clear line-of-sight, it isn't practical to use in an environment where
there are physical objects such as walls in between the devices to be connected.
B. RF: Two types of radio frequency communication were considered, namely
amplitude modulation (AM) and frequency modulation (FM). Both methods were
able to serve the needs of the project. Initially it was decided upon that a radio
frequency (RF) Transmitter/Receiver chipset would be used since RF technology
is available it seemed a good idea from a system level design perspective.
However, due to the cost of the chipsets and the relative size of this projects
budget it was decided that the transmitter and receiver would be designed and
built in order to minimize cost.
1. FM: Frequency modulation is achieved by transmitting a carrier signal
with constant amplitude and transcribing data into the frequency of the
carrier signal. The bandwidth required for the transmission of data using
frequency modulation can be obtained using Carsons Rule (Equation ()).
Carsons Rule determines the bandwidth (BW) required for transmission
using peak deviation (PD) and the highest modulated frequency (HMF).
The demodulation of FM signals requires a more complex receiver design
than that required for AM signal demodulation.
BW  2  ( PD  HMF )
(xx)
2. AM: Amplitude modulation is achieved by transmitting a carrier signal
with a constant frequency and transcribing data on the amplitude of the
carrier signal. The bandwidth required for the transmission of data using
amplitude modulation is found using Equation (). An AM signal can be
demodulated simply through the use of an envelop detector such as that in
Figure (). The output of the envelope detector often needs to be amplified.
BW  2  HMF
(xx)
Decision:(AM)
I.
Since the sensor is to be affixed to the neck of the Parkinson’s patient and the
speaker unit must be easily movable a direct line of sight between the transmitter
and receiver is difficult to maintain. It is also necessary to convert the analog
speech signal to a digital signal before it can be transmitted. A method of
transmission that does not require line-of-sight and can transmit analog data is
needed for this project and therefore IR transmission is not a viable option.
II.
One reason Amplitude modulation was chosen over frequency modulation
because only voice quality transmission is required. AM transmitter designs are
readily available, and the simplicity in design required for demodulating an
amplitude modulated signal made it an apparent choice. AM transmission does in
some cases require the use of more bandwidth than FM transmission but the
relative bandwidth needed for this project is relatively small and thus can be
disregarded in determining which method of transmission is to be used.
Design(work-in progress) and Simulation:
R6
TX3
330
V5
12Vdc
C1
.1u
C2
100p
R7
10k
C5
.1u
Q3
R10
Q2N3904
0
R8
2.2k
47u
C4
0
330
R9
1k
C3
.1u
0
0
V6
VOFF = 0
VAMPL = 3
FREQ = 1000
0
C6
.1u
Figure (): AM Transmitter Schematic
D1
Dbreak
C7
R11
.1u
1k
0
Figure (): AM Demodulator Schematic
The 1 kHz sinusoidal input signal of Figure () was applied to the AM transmitter circuit
of Figure (). The transmitter produced the amplitude modulated signal of Figure () with a
carrier frequency of 164 kHz as an output signal. The output of the transmitter circuit of
Figure () was then fed into the demodulator circuit of Figure (). The output signal
produced by the demodulator is of the same frequency as the input signal applied to the
transmitter circuit however they are not identical. This is because the transmitter design
is still in the process of being tweaked.
AM Transmitter Input Signal
4
3
2
Signal Level (V)
1
0
-1
-2
-3
-4
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
Time (sec)
Figure (): Test Signal applied to AM Transmitter of Figure ()
0.005
AM Transmitter Ouput (Amplitude modulated signal)
8
6
4
Signal Level (V)
2
0
-2
-4
-6
-8
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
0.005
Time (sec)
Figure (): Transmitter output when Test Signal of Figure () is applied
Demodulator Output
6.00
5.00
Signal Level (V)
4.00
3.00
2.00
1.00
0.00
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
Time (sec)
Figure (): Demodulator Output when Test Signal is applied
0.005
FCC Regulations (Article 47 - Part 15):
The maximum field strength at a given distance for a given carrier frequency as regulated
by the federal communications council (FCC) of an intentional radiator (transmitter) is
listed in Table 1.
To calculate the radiated field emissions use Equation xx, where PT is the transmitter
power in watts, GT is the transmitter gain, and r is the distance from the transmitter in
meters.
E
( PT  30  GT )
r2
Frequency (MHz) Field Strength (µV/m)
0.009 – 0.490
2400/F(KHz)
0.490 – 1.705
24000/F(KHz)
1.705 – 30.0
30
30 – 88
100**
88 – 216
150**
216- 960
200**
Above 960
500
(xx)
Measurement Distance (meters)
300
30
30
3
3
3
3
Table 1: FCC-Transmitter Radiated Field Emission Limits
To meet the FCC regulations for a transmitter with a carrier frequency in the range of 9
kHz to 490 kHz the product of the transmitter power and the transmitter gain must be in
the range of 14693.9 to 800000 watts depending upon the carrier frequency of the
transmitter involved. For the carrier frequency of 164 kHz that was used during
simulation the product of the transmitter power and the transmitter gain must be less than
or equal to 43902.4 watts to meet FCC regulations.