Smartphone "Music Player" High Fidelity Restore Solution

Smartphone audio quality should include two aspects: first, as the sound quality of portable communication devices; second, as a high-fidelity restore of the smartphone "music player". This issue of the program newsletter will be based on high-fidelity (Hi-Fi) audio quality, starting from chip selection, circuit design, processing algorithms, proposed NCN technology, equalizer filtering algorithm, PCB wiring skills, miniDSP Codec and MEMS device selection, etc. .

1. Sound quality of portable communication equipment

With the growing consumer segment of smartphones and the high quality of life that people bring to their smartphones, consumers are demanding that they can talk loudly and hear each other in noisy environments, and are immune to echoes. . As can be seen from various data, there are many factors affecting the audio effect, such as the introduction of high-resolution audio amplifiers, radio frequency interference, PCB wiring, and insufficient power, which can affect the call quality. These factors affecting the consumer's audio experience require manufacturers and system designers to integrate more advanced audio processing functions, including hardware and software, into portable communication devices, making voice calls in noisy environments even louder. Be heard clearly, and eliminate echoes. This has led to the pursuit of high-fidelity (Hi-Fi) audio processing solutions are more popular with consumers.

These requirements present challenges for designers because they typically must be completed in a smaller form factor and design constraints that do not affect power consumption (battery life), weight (battery size), and cost (especially sensitive to consumer equipment). The following are research and solutions for some of the above factors, and I hope to help engineers and developers:

Noise caused by the introduction of high-resolution audio amplifiers

Regardless of whether the network used by the mobile phone is GSM or TDMA, the switching action of the RF transmitter will seriously affect the noise of the power supply because the switching frequency of the RF power amplifier is 217 Hz. The amplifier draws a large amount of current from the power supply (typically up to 1.7A) per switch, resulting in a burst voltage drop of up to 500mV across the battery equivalent series resistance (ESR). For SoC designs with embedded high-resolution audio converters and audio amplifiers or highly sensitive MEMS, this change will jeopardize the overall performance of the SoC, especially as audio quality will be severely affected and audible noise will be heard. This document presents the concept of PSRR (PSRR stands for the ability of the regulator to maintain output voltage stability when the input voltage changes). It analyzes in detail the effects of PSRR and other power factor on the audio quality of the handset. example:

Radio frequency carrier interference

At present, there are more and more opportunities for audio amplifiers to be interfered with by RF strong electric fields. Many audio amplifiers are not designed with high frequency signal interference in mind, so it is easy to demodulate RF carrier information into the audio band, causing RF interference. This document presents several ways to reduce the effects of RF noise:

1. Integrate the audio amplifier into the baseband device

2, optimize the circuit board design

3, using audio amplifiers that are not affected by radio frequency

PCB wiring improves cellular phone sound quality

Cellular circuit board layout is a great challenge for PCB layout engineers. Modern cellular phones cover almost all portable subsystems, each with conflicting requirements. A well-designed PCB must take advantage of the performance advantages of each interconnected device while avoiding mutual interference between subsystems. Therefore, for each conflicting requirement, each subsystem performance must be compromised. Although the audio function of cellular phones continues to increase, little attention has been paid to the wiring of audio circuit PCBs. This document proposes the relationship between PCB layout and cellular phone sound quality, and reduces the call noise of smartphones from the wiring.

Advanced device selection to reduce call noise

More and more mobile devices, such as mobile phones, headsets, cameras and MP3s, use advanced noise reduction technology to eliminate background sound and improve sound quality. To this end, MEMS microphones from EPCOS are not only resistant to RF and electromagnetic interference, but also extremely small in size, making them an ideal solution for modern smartphone designs; Texas Instruments offers ultra-low-power miniDSP audio Codec integration The dual miniDSP core provides high-performance voice and music processing for battery-powered portable products with low power consumption.

2, smart phone "music player" high fidelity restore

In 2009, global shipments of Feature phones and Smart phones will exceed 1 billion units, accounting for more than 80% of all mobile phone shipments. In the current Chinese mobile phone market, the development of Feature Phone and Smart Phone is also the fastest. Among these mobile phones, the mobile phone speaker for music playback is already a standard configuration, and it can be said that most of the mobile phones are now music phones. “Want to sing and sing loudly” is a requirement for music phones, but now mobile phones have encountered many problems in music playback. Noise is introduced from MP3 source files, hardware design of mobile phone amplifiers, software design of players, etc. Thus, the original color is lost to the restored sound. The following is a technical overview of these factors in several ways:

Non-breaking (NCN) technology

The so-called NCN technology means that when the volume is increased or the power supply voltage changes, the loud sound in the music does not exceed the maximum undistorted amplitude, forming a broken sound, and the sound quality is "big without breaking." The Non-Broken (NCN) function uses Compression & LimiTIng in professional audio systems with important parameters such as threshold threshold, start-up time and release time.

Audio processing algorithm

Improving the audio quality of mobile phones is not an easy task. Two of the main factors are the size of the phone and the compression of the audio files.

Obtaining high-quality audio effects in the small size of mobile phones is indeed a challenge, and to meet this challenge can only be achieved by a cross-functional team composed of designers in the fields of industry, electromechanics and electronics. The engineer proposed this initiative: using audio processing algorithms. In compressed audio, audio is usually compressed into smaller files for users to download. File compression is implemented by an encoding algorithm (such as MP3). The reduction of files may result in the loss of information and ultimately affect the audio effect. Therefore, audio processing The algorithm can also come in handy.

Noise and its solutions

In portable multimedia devices in the current functional set, more and more functions are being integrated into smaller and smaller systems. Audio is the most basic function of any multimedia-enabled system on the market, but system designers are often more concerned with 'attractive eye' features such as wireless connectivity, video processing, image capture and display. As a result, where there is a little space between the many important components, the audio circuit is squeezed to where it is, resulting in very good or inferior audio quality. However, with a little attention, good audio quality can be seamlessly integrated into the system along with many other features that users demand. This article provides suggestions for excellent system design and PCB layout design related to any portable system design that includes audio playback and/or recording capabilities, as well as analysis of many of the analog audio that is present in portable audio systems that cause poor quality audio. A noise source that affects the sound quality of the signal.

HD voice technology

High-definition voice, also known as wideband voice, is an audio technology that delivers high-definition, natural voice quality for cellular networks, mobile phones, and wireless headsets. Compared to traditional narrowband phones, HD voice greatly improves voice quality and reduces the hearing burden. As narrowband networks and devices transition to high-definition voice, a voice processing technology called Bandwidth Extension (BWE) can be used to simulate call quality similar to HD voice on the receiving terminal device, providing a device that does not support HD voice. A compromise solution. This article will detail the BWE technology.

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