Hi-Fi audio will become a portable device, the next big thing for smartphones

With the breakthrough of many technological breakthroughs and new streaming music services, Pro Audio Hi-Fi is brought to mobile devices, and the future is very bright for smartphones, tablets and other mobile devices. Just as HDTV has changed the way people watch TV, Hi-Fi audio will be the next big thing for portable devices, especially smartphones.

In fact, many changes have taken place in optimizing the sound quality of mobile devices. Hi-Fi audio can reduce the effects of noise, distortion or other digital interference, such as front bell sounds, although the audience may not be aware of it, but it will undoubtedly affect their listening experience. Drivers and enhancements will bring a "black record-like texture" to mobile sound quality without consuming too much power.

The first indicator pointing to Hi-Fi audio is the increase in streaming music subscriptions. According to a report from the MIDiA Research Streaming Music Subscribers in December 2016, the number of streaming music users has doubled from 2014 to 2016, from 41 million users to 100 million. It is expected to reach 277 million by 2020. In addition, the BuzzAngle 2016 American Music Industry Report pointed out that in 2016, the average daily traffic of any day in the United States (an average of 1.2 billion per day) was more than the number of songs downloaded throughout the year (733.4 million). MIDiA data shows that streaming services represented by SpoTIfy (43 million subscribers), TIdal (about 1 million), Deezer (6.9 million) and Apple Music (20.9 million) are leading the market. Currently, only TIdal and QobuzTM provide Hi-Fi streaming, while Deezer, Soundcloud and JooxTM offer partial Hi-Fi sound. If big companies like SpoTIfy, Apple and Amazon start offering Hi-Fi streaming, then the market is expected to grow substantially. According to SAR Insight&Consulting1, by 2020, high-resolution audio (HRA) downloads will increase from 1% (2016) of global music downloads to 11%.

Figure 1. SAR Insight&Consulting predicts that by 2020, high-resolution audio downloads will increase to 11% of global music downloads.

Under the guidance of early adopters, these services will awaken users to a completely different music experience that they can't experience on current smartphone devices. But why is the sound quality of current smartphones or other mobile devices so bad? This is related to the physical limitations of mobile products: size, weight and battery life. At present, various technical restrictions are intertwined, hindering the application of cost-effective Hi-Fi audio on portable devices, but this situation is changing.

How is “Hi-Fi” audio defined? Simply put, it is low noise and low distortion audio as close as possible to the original music source. On a more technical level, Hi-Fi audio refers to the bit rate that allows "lossless" sound transmission. In order to compress music, the system ignores sounds that it thinks are inaudible to the human ear to save storage space. However, this "lossy" compression, or MP3, does reduce the audio quality because the human ear can actually discern this difference.

This explains why general users can hear "differences" when listening to compressed music on some portable devices, but don't know why. There are other challenges when transferring Hi-Fi audio to mobile devices. In the past, mobile devices did not have enough storage. It’s just that now, smartphones have enough storage to keep up with the higher resolution audio. In fact, the storage capacity of mobile products has grown exponentially over the past few years, so storing large amounts of lossless audio files, such as free lossless audio codec (FLAC) files, is no longer a problem. This means that users don't have to compromise on audio quality to be able to store multiple albums on their phones. In addition, many online music storage companies now allow users to download and arbitrarily delete songs and albums, eliminating the need to store the entire music collection on their phones.

Audio chip designers are also constantly developing and striving to integrate high-performance functions into lighter components. These components are not only smaller in size but also consume less power, maximizing battery life. Size and power consumption are physical factors required for a lightweight smartphone or wearable device. Other technical audio design elements are used to optimize compressed music and streaming media playback.

Consumers may be concerned about specific specifications, and specifications can indeed provide a good reference for the ability of products to reproduce high-quality audio. However, high quality audio is more than just specifications. In addition to reaching certain data levels, such as 16-bit/96 kHz or higher, there are many subtle additional factors that need to be considered in reproducing clear Hi-Fi audio. These factors can have a huge impact on audio quality.

For example, jitter can destroy the quality of the reproduced audio. All clock signals are affected by jitter. In a typical system, if the total amount of jitter is below -105 dBFS, the jitter is not heard. Clock performance is a must in the beginning of an audio system, and in essence it must be part of the audio system's DNA. This includes providing an accurate reference clock or designing an IC around a dedicated precision frequency-locked loop (FLL) to compensate for inaccurate reference clocks. The on-chip FLL provides a low jitter clock reference for the internal digital-to-analog converter (DAC) and amplifier by locking the external reference and providing a low jitter alternative to the original reference clock.

Originally designed for high-performance DACs, advanced Hi-Fi filters are used in many high-end professional audio systems and are now used in intelligent codecs for portable applications. This means that smartphones, tablets and other products can now enjoy the natural sound.

A well-designed Hi-Fi filter minimizes the effects of digital signal processing. The figure below is a graphical representation of the advanced 512-unit DAC architecture that sequentially filters out noise to help eliminate the effects of the digital world and provide the natural sounds people want to hear.

Figure 2 512-element DAC icon in Cirrus Logic CS 43130

In addition to reducing jitter, which affects the sound, the filter also changes the roll-off and phase response, eliminating the front bell. For example, the sound of a collision is usually something that people don't want to hear, because its sound is always unclear and accompanied by some noise when it starts to hit.

Did I hear the front bell?

The front bell is artificially created during the digital processing process, causing people to hear some sound before the real sound appears. This means that the sound is not as clear as it should be. In the real world, there is no sound that can emit the front bell, and the human ear is also very sensitive to the front bell. If the filter does not function properly during the digital-to-analog conversion, the reproduced sound tends to be blurry, dull and dull.

The following figure shows how to remove the front bell through the filter by using the real effects of the Cirrus Logic CS43130 low-power DAC and provides a range of filters to choose from. The visible sound waves in the left image can be considered as the primary audio signal (such as drumming). The rear bell vibrates the sound that does exist in the real world after the sound is generated, such as the vibration after the drum is hit. However, the pre-ring ringing wave is the result of the failure of the audio filter operation during digital processing. As shown on the right, advanced Hi-Fi filters and filters with a wider range of variations eliminate front bell vibrations, making the rear bell vibrations more varied and natural, delivering high-quality sound.

For distortion-free natural-sound digital audio, dynamic range is another very important factor in audio engineering. The human ear has a wide dynamic range and can hear very light sounds and very loud sounds. This volume range is called the dynamic range.

For the maximum signal range to be reproduced correctly, the high dynamic range of high performance DACs is critical. If the dynamic range of the DAC is very low, especially at less than 96dB, the user will hear the digital noise floor when the volume is increased. The dynamic range of a typical 16-bit MP3 file is 96dB. In today's advanced Hi-Fi audio format, the dynamic range of 24-bit FLAC is 144dB, and the dynamic range of 32-bit audio is also wider. (FLAC is an audio format similar to MP3. The difference is that FLAC is lossless, meaning it is not damaged even if it is compressed.) By providing a dynamic range of up to 130dB, in all amplifier gain settings, The smallest and largest digital signals can be transmitted without being affected by the noise floor.

Listening to digital music on mobile devices is becoming more and more popular around the world, and using these audio technologies in portable devices is just the right time. The "2016 China Music 360 Report" recently released by Nielsen fully proves this. According to the report, 72% of Chinese people listen to music on average 16 hours a week, millennials even up to 19 hours; 66% of music listeners (69% of millennials) listen to music on their smartphones. As a country with more than 1 billion people, the situation in one country in China indicates a huge growth potential in the field of smart phone audio, and smartphone manufacturers are also paying close attention to this trend. The emergence of streaming music services and the growth of subscribers and the popularity of Hi-Fi audio have further boosted the demand for Hi-Fi audio for mobile devices. While chip technology providers are still struggling to overcome chip limits, storage capacity, battery life and many other limitations on mobile platforms, audio device designers have opened the door to new technologies to enhance the user's listening experience. That's why Hi-Fi audio is the next market focus after smartphones, tablets and wearables. Bringing high-quality professional audio to mobile devices is not far off, and is here to come.

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