What is the basis of a high-definition audio system?

In response to customer demand for top-tier audio quality, audio system designers are investigating high-resolution or high-definition (HD) audio, as more and more mid-range system buyers demand the type of HD audio performance that was previously only available in high-end systems. In the past, 44.1kHz CD-quality sampling frequencies were sufficient for much of the market, but today (and for the foreseeable future), the demand for high-fidelity sound will only continue to grow.

According to professional and consumer audio equipment companies, higher sampling frequencies capture and reproduce a wider frequency range. The reproduction of audio frequencies greater than 20kHz, including ultra-high frequency harmonics, gives the characteristics of the subtle components of sound (especially acoustic instruments). According to these audio equipment companies, there are some technical advantages that make it worthwhile to move to higher sampling frequencies, such as the reduction of unwanted side effects due to the steep filters employed during digital-to-analog conversion or analog-to-digital conversion.

Simply picking up an off-the-shelf music player will not deliver on the promise of high-resolution audio, which requires specialized hardware to truly enjoy its richness and subtlety. Of course, not every audio file or media is recorded in high-definition audio.

Designing High-Definition Audio Systems

As with every high-performance design, taking a full-system approach to the entire audio signal chain ensures a robust and high-performance solution. Because every link in the audio signal chain is important, ensuring it has no weakest link, each link must be able to meet all design target specifications such as performance, cost, time to market, and ease of use. Figure 1 shows the foundation in an HD system.

Figure 1: High-definition audio system

The power management block provides the correct power level to the Wi-Fi® speaker circuit. Assuming the application is system powered (not battery powered), and depending on the output power, the power supply not only needs to provide the voltage and current required to meet the system power requirements; it also needs to provide a clean and stable power rail to prevent any power supply noise from entering the audio system and degrading the audio quality.

Connectivity modules provide wireless communication to the system using Wi-Fi or Bluetooth® via a computer, smartphone, tablet or wireless-enabled product. Standard Bluetooth modules today offer an all-in-one solution for portable audio systems, as they natively support both wireless and wired audio. But their limited bandwidth poses a potential bottleneck as lossless high-resolution audio streaming requires higher bandwidth. New Bluetooth audio coding technologies promise increased bandwidth to support high-definition audio.

On the other hand, Wi-Fi includes greater network capacity, powerful signaling, and a wider wireless radio range. Its increased bandwidth capacity and system throughput make it more suitable for high-definition audio applications.

The processor performs various audio processing functions, such as decoding and signal equalization, while also handling the Wi-Fi and/or Bluetooth communication software stack. In the past, CD-quality sampling frequencies may have been sufficient. However, today's high-fidelity audio systems place additional demands on the processors in the signal chain, as high-fidelity sound quality requires sampling rates ranging from 48kHz to 192kHz in a 24-bit music signal stream.

The audio module contains all the electronics needed to drive the speakers in the system. Because the signals from the connection module and the processor have low voltage and low current capabilities, the audio amplifier provides the necessary higher voltage and current capabilities for the signal to drive the drivers in the speaker system. The module can include an audio digital-to-analog converter (DAC) to convert the digital audio signal from the processor to an analog audio signal and provide other audio processing in the digital domain to further enrich the customer experience in high-end systems. Another key component of the audio module is the audio amplifier.

Audio Amplifiers: Class AB vs. Class D

为您的高清音频系统选择最佳音频放大器时，您有两种选择：AB类或D类。AB类音频放大器是线性放大器，无需许多外部电子元件。但是它们的效率极低，并且需要以散热片和风扇的形式进行大量无源或甚至是有源的热管理。

Class D audio amplifiers, on the other hand, are highly efficient switching amplifiers that require little thermal management, but they do require an output inductor.

For many years, amplifiers in HD audio were Class AB amplifiers. Audio Class D amplifiers were considered substandard because they did not meet all the requirements for HD audio; today they no longer exist. TI's latest generation of Class D amplifiers improves the overall performance and efficiency of HD audio systems by creating a symbiotic relationship with the digital engine while efficiently transmitting enhanced audio quality to the speakers.

Optimized HD audio design

High-performance, high-definition audio amplifiers with integrated DAC and processing, such as TI's new TAS5782M, can help audio designers greatly simplify designs, reduce costs and shorten design cycles. The integrated DAC helps reduce system complexity by providing a way to connect the audio amplifier directly to the processor, ensuring maximum signal integrity and reducing component count.

Integrated audio processing can greatly help reduce the cost and computational requirements of the main application processor by offloading all audio processing into the amplifier itself. You can further reduce cost and size by reducing the cost and size of the main processor. Figure 2 is an optimized block diagram.

Figure 2: Optimized HD audio system

Do you design high-definition audio systems? If so, what specifications are most important to you?