1. Advanced Science and Technology Letters Vol
Advanced Science and Technology Letters Vol.94 (Mobile and Wireless 2015), pp
Design of Wireless Digital Audio System with Noise Cancellation Algorithm
Joon-Hoon Park
Dept. of Control & Instrumentation Eng., Korea National University of Transportation,
Korea
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.
ISSN: ASTL Copyright © 2015 SERSC

2. 2 Design of Wireless Digital Audio System
Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)
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 v5. Sinusoidal signal v5 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.
Copyright © 2015 SERSC 23

3. 3 Design of Noise Control Algorithm
Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)
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]
1 2
1 0 8 6 4 2
D is ta n c e (M )
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
24 Copyright © 2015 SERSC

4. 4 Conclusions References
Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)
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), ̃() is gained source signal by U(s) and ̃() 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
̃() =∑ ̃
=0∅ (, ) (2)
=0∅ (, ) (3)
() = ∑ [
=0 − ]
∅(, ) (4) where ∅ () 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]
( + −1 +⋯+1−1+ 0)∅()
≅ ( + −1+⋯+1−1+ 0)∅() (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 H1C1A ).”
References
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, , (2008).
B. Widrow: Adaptive Noise Cancelling: Principles and Applications, Proc. IEEE, Vol. 63, , (1975).
Copyright © 2015 SERSC 25

5. http://www.ti.com/product/TPA3003D2/technical documents
Advanced Science and Technology Letters Vol.94 (Networking and Communication 2015)
W. M. Leach: Introduction to Electro Acoustics and Audio Amplifier Design- Second Edition, Kendall/Hunt Publishing, (2001).
documents
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).
J. H. Park: Transfer Function Approximation using Rationalized Haar Transform in Frequency Domain, Int. J. of CA, Vol.7, No.4, 247, 258 (2014).
26 Copyright © 2015 SERSC