Design of Wireless Digital Audio System with Noise

Cancellation Algorithm

Joon-Hoon Park

Dept. of Control & Instrumentation Eng., Korea National University of Transportation,

Korea

jhpark@ut.ac.kr

Abstract. On the basis of digital electronics technology digital audio system is

used to reproduce audio signal and amplitude original signal level. So since the

1970s, digital signal and audio system technology have rapidly replaced

existing analog audio signal and system in most areas especially mobile and

wireless fields. Moreover because of trend of mobility, many electronic

products have been downsized and further improved. In this paper, a design

technology is introduced to implement compact and wireless digital audio

system with noise cancellation algorithm based on the orthogonal transform.

The proposed digital audio system is shown good operational characteristics

such as signal distortion and efficiency and simple adaptive noise cancellation

algorithm.

Keywords: digital audio system, wireless transmission, mobility, noise

cancellation, orthogonal transforms

1 Introduction

The audio sound system was invented in 1909 by Lee De Forest when he invented the

triode vacuum tube. Then the modern audio system as the basis for a transistor or

digital signal processor with the development of digital technology has been popular

items, with a wide range of applications. In general, audio system can be classified

into following four types, Class-A, B, AB and D type according to system

characteristics. In a Class-A type, bias current flowing in the output appear so its

efficiency is about 20%. The Class-B type operates in the opposite way of the Class-A

system to improve system efficiency. And the Class-AB is a combination of the

Class-A and B type, and is one of the most common types of existing power audio

system. In a Class-D type, a switching or PWM(Pulse Width Modulation) technology

was applied because switches are either fully on or fully off and power losses are

significantly reduced in the output devices.[1] However, there must be a noise and

this noise has a negative impact on a system. To improve these problems, noise

cancellation algorithm is proposed and applied to a digital audio system design.

Basically noise cancellation method emits a sound wave with the same amplitude but

with inverted phase to the original sound.[2] For this, rationalized Haar function and

transform are suggested in this paper.

Advanced Science and Technology Letters Vol.94 (Mobile and Wireless 2015), pp.22-26

http://dx.doi.org/10.14257/astl.2015.94.06

ISSN: 2287-1233 ASTL Copyright © 2015 SERSC

2 Design of Wireless Digital Audio System

2.1 Class-D Type Amplifier

As mentioned above the main difference between linear types and Class-D is the

efficiency. This was the entire motive for the invention of Class-D type. Now let’s

consider an input signal is a standard audio line level signal vs. Sinusoidal signal vs is

wave with a frequency ranging from 20Hz to 20KHz typically. This signal is

compared with a high frequency triangle waveform vt to create the PWM signal vp.

This PWM signal is then used to drive the power stage, creating the amplified digital

signal, and finally a low pass filter is applied to the signal to filter out the PWM

carrier frequency and retrieve the sinusoidal audio signal vo. The sound source is

amplified and reconstructed through the system.[3] The voltage waveforms are shown

in fig. 1.

Fig. 1. Voltage waveforms

2.2 A Digital Audio System with Wireless Feature

In this paper, the 3W/stereo Class-D audio amplifier TPA3003D2 of TI(Texas

Instruments) is used to design and implement a digital audio sound system.[4] The

TPA3003D2 can drive stereo speakers as low as 8Ω. The high efficiency of the

TPA3003D2 eliminates the need for external heat sinks when playing music and

stereo speaker volume is controlled with a dc voltage applied to the volume control

terminal. Its block diagram is shown in figure 2. And Bluetooth technology is applied

to add wireless sound transmission and mobile features. As we know, Bluetooth is

worldwide standard technology for wireless exchanging data over short distances.

Bluetooth is a packet-based protocol with a master-slave structure. One master may

communicate with up to seven slaves in a piconet. In this system, Bluetooth v4.1 is

used that is announced by the Bluetooth SIG in December 2013.

Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)

Copyright © 2015 SERSC 23

Fig. 2. Block diagram of TPA3003D2

In figure 3, block diagram of proposed wireless digital audio system (WDAS) is

shown. And designed WDAS has 30dB of signal to noise ratio, 70dB of channel

separation and 40~20KHz of frequency response.

Fig. 3. Block diagram of designed wireless digital audio system

For optimal utilization of Bluetooth v4.1, Bluetooth wireless data transmission

experiment is carried out according to various environmental conditions. One of the

results obtained by this experiment, recognition time between Bluetooth transmitter

and receiver is changed from 77m sections by each baud rate change. In this case,

data transmission is very stable and fast. But the results depend on a change in the

surrounding environment. For example, wireless data transmission result is received

bad influence by a microwave or noise. One of the Bluetooth transmission test results

is shown in figure 4.[5]

Fig. 4. Wireless data transmission experiment and its results

3 Design of Noise Control Algorithm

As mentioned in chapter 2, wireless data transmission is influenced by various

environments. Therefore noise cancellation algorithm using the rationalized Haar

D is ta n c e (M )

6 0 6 2 6 4 6 6 6 8 7 0 7 2 7 4 7 6 7 8

Tim

e(S

ec

)

0

2

4

6

8

1 0

1 2

4 8 0 0 b p s

9 6 0 0 b p s

1 9 2 0 0 b p s

Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)

24 Copyright © 2015 SERSC

function and transform is proposed for noise cancelation in this paper. The u(n) is

signal source and r(n) is noise source. U(s) is transfer function of first acoustic path

from signal source and P(s) is transfer function of filter from output p(n). And e(n) is

residual error signal from error sensor and desired output signal y(t), (𝑛) is gained

source signal by U(s) and 𝑝(𝑛) is gained and filtered signal by P(s). Noise

cancellation is a change in the optimal filtering includes generating noise estimate by

filtering the reference input and then subtracting this noise estimate from the primary

input containing both signal and noise. Now we can express the noise cancellation

algorithm using rationalized Haar function as

(𝑛) = ∑ 𝑖𝑚𝑖=0 𝑃𝑅𝐻𝑖∅𝑅𝐻(𝑖, 𝑡) (2)

𝑝(𝑛) = ∑ 𝑖𝑚𝑖=0 𝑃𝑅𝐻𝑖∅𝑅𝐻(𝑖, 𝑡) (3)

𝑒(𝑛) = ∑ [𝑈𝑖𝑚𝑖=0 − 𝑌𝑖]𝑃𝑅𝐻𝑖

𝑇 ∅𝑅𝐻(𝑖, 𝑡) (4)

where ∅𝑅𝐻(𝑡) is rationalized Haar function and PRH is operational matrix with t= m

Then desired output y(t) can be obtained from equation (5) and we can determine

parameter a and b for noise cancellation system.[6]

𝑌𝑇(𝑎𝑝𝐼 + 𝑎𝑝−1𝑃𝑅𝐻 + ⋯ + 𝑎1𝑃𝑅𝐻𝑝−1

+ 𝑎0𝑃𝑅𝐻𝑝

)∅𝑅𝐻(𝑡)

≅ 𝑈𝑇(𝑏𝑞𝐼 + 𝑏𝑞−1𝑃𝑅𝐻 + ⋯ + 𝑏1𝑃𝑅𝐻𝑞−1

+ 𝑏0𝑃𝑅𝐻𝑞

)∅𝑅𝐻(𝑡) (5)

4 Conclusions

In this paper, a design method of wireless digital audio system with adaptive noise

cancellation algorithm is proposed. For this, Class-D type amplifier, Bluetooth

technology and rationalized Haar transform are applied. The operating and electronics

characteristics are shown good results. And algorithm for noise cancellation system is

simple and useful to build system hardware and firmware.

Acknowledgement. “This research was financially supported by the Ministry of

Education (MOE) and National Research Foundation of Korea(NRF) through the

Human Resource Training Project for Regional Innovation (No.

2014H1C1A1066414).”

References

1. J. H. Park, S. D. Jang and Y. G. Choi: Development of a mobile digital audio system using

TPA2008D2 and secondary battery, J. of KIIT, Vol.6, No.3, 129--38, (2008).

2. B. Widrow: Adaptive Noise Cancelling: Principles and Applications, Proc. IEEE, Vol. 63,

1692--1716, (1975).

Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)

Copyright © 2015 SERSC 25

3. W. M. Leach: Introduction to Electro Acoustics and Audio Amplifier Design- Second

Edition, Kendall/Hunt Publishing, (2001).

4. http://www.ti.com/product/TPA3003D2/technical documents

5. J. H. Park and R. D. Oh: Implementation of Digital Stereo Amplifier for Mobile IT Devices

based on Wireless Communication System using Bluetooth, ICMOCCA 2007, (2007).

6. J. H. Park: Transfer Function Approximation using Rationalized Haar Transform in

Frequency Domain, Int. J. of CA, Vol.7, No.4, 247, 258 (2014).

Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)

26 Copyright © 2015 SERSC