Let’s talk audio – Wolfson Q&A

August 13, 2014
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Chances are, your smartphone and tablet have become integral parts of your day to day media experience, and many of you have probably already thrown out your old MP3 player in favor of your smartphone. Year on year, we are demanding more and more from our smart devices, particularly when it comes to audio. With that in mind, we had a little Q&A session with one of the leading suppliers and developers of audio semiconductors and electronics, Wolfson Microelectronics.

If you own Exynos versions of Samsung’s modern Galaxy S devices then you have probably had the pleasure of listen through a Wolfson DAC, and the company made the news not too long ago when it announced its 24-bit 192kHz Audio Hub for mobile devices. But what about the future, can we squeeze even more audio goodness from our smartphones?

Q – What is the current state of audio quality and smartphones? What are some positive or negative trends in the industry?

A - There has been tremendous improvement in audio quality in the last 4-5 years. The gap from hi-fi quality sound to what is available in a handset has become quite narrow. If you plot the specification requirement in terms of what OEMs are looking for, it’s radically increasing year on year, i.e. every year OEMs are not asking for it to be slightly better; they’re looking for it to be substantially better. These days, it’s not only about the parameters, it’s also about the function you offer.

While audio quality has mainly been seen as a differentiator for an ultra-high-end phone, the big difference now is that audio quality is being seen as an important feature across the entire product line.

samsung galaxy s5 vs htc one m8 aa (12 of 19)

HTC’s front facing speaker design is still leading the pack, in terms of sound quality.

This is certainly true, in a number of different ways. From a hardware perspective, we have seen HTC up its game with its BoomSound front facing stereo speaker setup in its One series, which offers up a cleaner listening experience than traditional rear facing speakers seen in other smartphone models. On the software and DAC side of things there is increasing demand and support for higher quality audio formats in recent years, such as lossless FLAC files and high resolution 24-bit 192kHz audio. With that in mind:

Q – FLAC vs MP3 – what’s the difference?

A – FLAC is lossless, and MP3 is not. With FLAC, we’ve observed that people tend to hear lyrics or details in the recording that would be lost in an MP3 … The original artist has an almost infinite range of expression, and we find that there are things that are captured by the FLAC that are not captured by the MP3. We believe FLAC is better because it’s a truer representation of what was actually recorded and it sounds more natural.

With MP3, there’s a loss of some detail and an addition of some detail that was not on the original master track. There’s more distortion in the file, you just don’t notice it because of masking. There’s an idea that if you hear a loud noise, you don’t hear a quiet noise after it. So, with an MP3, every time there’s a loud piece of music, masking means you don’t need to accurately represent the softer or quieter detail, so the file is smaller. It may not be true for everybody, but if you know what to listen for, the artefacts are very noticeable.

Audio Masking

The human ear is not sensitive enough to detect nearby frequencies which differ in amplitude by a certain loudness/threshold. By removing the inaudible parts of the signal, MP3s can reduce their file size substantially compared with the original file.

Steinberg

To further elaborate on the characteristics of the MP3, although some parts of the signal may not be audible anyway, removing these parts of the signal creates additional distortion to the original waveform. There’s also a question of sound and tone too, lower amplitude harmonics are important parts of a sound or tone. Furthermore, additional color created EQs, pre-amps, or listening environments will not be able to pick out the detail removed from an MP3 file, which means that tonal qualities and details are lost that may have been enhanced further down the signal chain.

Lossless compression systems, like FLAC, instead focus solely on optimising the coding format, leaving the audio signal completely intact. In the pursuit of even more detailed and accurate reproductions of analogue audio signals, higher bit depths and faster sample rates are becoming more common, such as 24-bit 192kHz audio.

“As flash memory becomes cheaper, we can move to higher sample rates, so that your source material no longer limits you.”

The MP3 may have gained popularity in the days of limited digital storage space and slower internet download speeds, but these days we can easily store larger, lossless file sizes on our multi-GB smartphones and microSD cards.

Q – Do hardware partners see audio quality as a crucial part of mobile these days? For example, LG made a big fuss about its 192kHz audio capabilities when it launched the G2.

A - Audio is one of the few ways left for mobile device manufacturers to differentiate their products. Twenty years ago, people would have had two large stereo systems and possibly a cassette player in their home, however, most people’s exposure to music these days is on their mobile device.

As well as offering Master Hi-Fi™ (24-bit/192kHz), we also offer a suite or a menu of options, such as noise cancelling to help the clarity of conversation, improved audio playback and audio recordings; this enables customers to differentiate their products in a market where phones look rather similar.

Let’s quickly explore what is meant by this move towards Master Hi-Fi quality. Common audio formats all store audio data by collecting samples at a repeated period in the time domain (sample rate in hZ) and record the waveform’s amplitude with limited accuracy (bit depth), with the exception of Direct-Stream Digital, but that’s not so common. As the upper limit of human hearing is around 20kHz, a sample rate of around 40kHz allows for a full reproduction of the human hearing range. However, this only results in on and off (square wave) values at very high frequencies, rather than full waveform capture, which some will argue results in an audible loss of accuracy at high frequencies.

Bit-depth, on the other hand, allows for a higher resolution capture of amplitudes. Low bit depth approximates different amplitudes to the same loudness, whilst higher bit-depths retain a wider range of amplitudes. While 16-bit CD quality allows for 65536 different amplitude values, 24-bit audio allows for a massive 16777216 different amplitudes, capturing and reproducing audio in even more detail.

Q – How do you elevate consumers’ understanding of the audio chips behind the smartphones? Unlike SoCs and RAM, audio chips are regrettably left out of most spec sheets. Where do consumers go to get this sort of info?

A – Specifications for audio aren’t necessarily the right thing to focus on. It is more than just numbers. For example, valve amplifiers have large amounts of harmonic distortion and the audio specifications don’t measure as well as some modern solid-state amplifiers, however some people think they are “warm” and sound great.

Audio ought to be natural. You almost wouldn’t want people to think about the chip inside their device; you just want them to have the best possible listening experience. It comes down to: what’s the role of good audio? I would say that it’s to be transparent.

It’s interesting to use the word transparent, especially when we look at some more recent attempts at high-end smartphone audio hardware. HTC’s, or I guess that should now be Apple’s, Beats Audio is notorious when it comes to additional bass tonal qualities. Also, the mention of valves is an interesting one, as they certainly can’t be described as clean, yet are often found in high-end audio equipment.

Valve and SSL

The debate over valves and solid state has been running for decades. Throw digital into the mix, and it’s no wonder that audiophiles can never agree.

However, audio is often about preference, and a transparent DAC is important, as it allows the user to tweak their sound to their own preferences without the DAC making the decision for them, be that through EQ settings or headphones.

Q – What are the factors that limit audio quality on smartphones?

A - Small form factor means that space is a premium and components get squeezed into a small area. Ultimately, audio only performs as well as the weakest link in the chain and, to some extent, the weak link tends to be the headphones in terms of audio reproduction. Quite often, on a bad PCB design, it can actually be the integration of the chip, the power and the routing that manifestly affects the audio quality you get.

Q – What’s your personal recommendation of a smartphone for users interested in the best possible audio? What about headphones?

A – We wouldn’t recommend a particular smartphone, however the biggest problem when listening to music on a smartphone through headphones is that the background noise gets in the way. What you really need is a set of noise cancelling ear buds. At the moment, we’re the only company to offer +/-1dB sensitivity for multi-microphone applications. Our microphones have a very uniform sensitivity, and without that a lot of processing power would be burned to compensate for the mismatch.

Personally, we think open-back earphones are the best in terms of response, however they’re leaky, so the person sitting next to you will likely be able to hear what you’re listening to. The one advantage of an ear bud is that, you can get a really good suppression just by blocking the ear canal. The best headphones depend on your environment.

Open-back headphones are known for their superior response mainly as there is equal air pressure on both sides of the speaker cone, allowing it to move freely and reproduce the sound accurately. Close-back headphones and in-ear earphones, on the other hand, offer up a barrier between the listen and the background noise, but can suffer from slight distortions as the air pressure in front of and behind the speaker changes, and can also end up with a boxy sound as the ear is completely enclosed.

bose-soundtrue-sg-1

Noise cancelling headphones try to offer up the best of both worlds, allowing more free movement of the speaker cone whilst still managing to eliminate most of the background noise. However, the trade-offs come from the active nature of noise cancellation, which requires external power, as well as the limited threshold for background noise.

If you’re in the market for the perfect pair of headphones, our partners over at Sound Guys have you covered.

Q – What are the upcoming technologies that you are excited for, as audio experts?

A - We’re looking forward to the future of our Ez2 software, including our ‘always on’ feature, and seeing this integrated into more devices. Our Ez2 suite of software solutions is augmented by Wolfson’s Partner Programme.

Our partners include:

Audyssey Laboratories, with its AudioFrame™ advanced audio recording technology, which ensures that the recorded audio signal on a mobile device dynamically adjusts to match the video zoom.

ComHear, with its Kinetic Audio Processing (KAP™) software combined with Wolfson’s Audio Hub solution with Ambient Noise Cancellation (ANC), delivers rich and clear audio experiences for the wearable consumer space.

Elliptic Labs, with its ultrasonic gesture control solution combined with Wolfson’s ADSP platform, makes ‘always on’ ultrasonic, low power touchless gesture control a reality for consumer electronics devices such as smartphones and tablets, as well as for in-car infotainment.

Fortemedia, with its ForteVoice™ advanced multi-microphone voice processing technology combined with Wolfson’s ADSP platform, enables seamless voice communication on smartphones and tablets whether the user is in a car, a busy street or a crowded restaurant.

Malaspina Labs, with its VoiceBoost™ ‘always listening’ voice activation solution and phonetic speech enhancement technologies combined with Wolfson’s Audio Hub solution, delivers an enhanced hands-free voice calling experience on a mobile device, even in noisy environments

NXP Software, with its LifeVibes™ VoiceExperience 4.0 technology combined with Wolfson’s ADSP platform, provides natural speech for any calling use cases, including speakerphone calls, even in the noisiest environments.

Sensory, with its state-of-the-art TrulyHandsfree™ ultra-low power voice control solution, combined with Wolfson’s Ez2 control™ software, removes the need for physical button-push activation as required in current voice control applications

Waves Audio, with its MaxxAudio® Mobile sound processing software combined with Wolfson’s ADSP platform, helps to bring exceptional audio quality and extended playback time to laptops, tablets and mobile devices

A big thanks to Wolfson for taking the time to answer our questions. It looks like there’s a lot more to look forward too on the portable audio front, and not just in terms of listening quality. We’ve heard from the experts, but how important is audio to your smartphone experience? Has it becomes an increasingly important factor in your purchasing habits?

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