Tracing the Key Milestones in Digital Audio

Author : Dan Knighten, General Manager of Audio Precision

29 January 2024

There have been dramatic changes within consumer and professional audio space over recent decades, with 3 particular trends featuring prominently. These are the widespread proliferation of digital audio, the addition of audio to everyday appliances and the dispersal engineering teams (which now significantly complicates design/testing processes). This article delves into these trends and the transitions to the digital audio landscape that have resulted.

Trend #1: The digital audio takeover - How ones and zeroes rose to dominance
Compact discs (CDs), which started to become popular in the mid/late 1980s, gave us the first mainstream digital audio storage medium. By encoding music within bumps and pits representing binary code, CDs vastly expanded both sound fidelity and operational practicality compared to previous analogue formats, like vinyl discs and cassette tapes. Nowadays you cannot find a consumer or professional audio device that doesn’t leverage digital inputs/outputs in some form. Whether connected through HDMI, Bluetooth, or various audio over wired or wireless network options, the audio signal is being transported digitally via I2S, PDM and other low level serial data formats. One way or another, audio is almost always digital until very close to the acoustic transducer (speaker or microphone) in a device.
 
And that is unsurprising - as analogue audio is hard. Filters and equalisation must be handled by complex networks of resistors and capacitors. Maintaining signal fidelity, avoiding crosstalk and mitigating other degradations requires careful design layout and component selection. There is also much more susceptibility to errors from manufacturing tolerances, etc. Once an analogue signal is translated into digital form, then a plethora of signal processing/conditioning options become available. While digital signal processing (DSP) is susceptible to errors, it is not vulnerable to analogue interference - such as polluted ground planes, capacitive crosstalk, common mode noise or the many other issues that require well thought-out design when working in the analogue realm. While processing digital audio is not easy and more than a few engineers will miss subtleties, nevertheless digital audio tends to present one-time challenges, such as figuring out how to implement the necessary signal processing. Once addressed, perfectly reproducing that audio is not actually so much of a problem.

As an example, every time a vinyl LP is played, the audio produced changes - since the very process of playing a record slightly degrades the analogue media. Conversely, not only can a digital music file be played an infinite number of times without any degradation, but every copy of that file is completely identical. 

Trend #2: How appliances found their voices
Until recently, appliances merely emitted beeps and hums. However, the era of smart devices has transformed mundane products by enabling bi-directional vocal interactivity through integrated microphone arrays and speakers. Where audio quality was once irrelevant, domestic items like refrigerators now stream content and washing machines articulate status updates verbally. As a consequence, audio performance thresholds continue to rise, with developers confronting new competency demands in disciplines historically audio adjacent. What has happened, without anybody really acknowledging it, is we've added audio to a vast swathe of devices that used to be dumb - quite literally in both senses of the word. 

Trend #3: Bridging the gap between hardware and firmware engineers
Long gone are the days of electrical engineers wielding sole mastery over hardware and software. Most companies now have dedicated specialist teams for product architecture, design, layout, embedded firmware, FPGAs and DSP development. This fragmentation into discrete groups with divergent tools and particular working practices has created a divide between hardware engineers probing circuit boards in the lab and their coding counterparts creating programs and algorithms.
 
As the global COVID-19 pandemic exiled collaborators to home offices - separated by continents rather than cubicles - the physical and workflow division between domains has led to a complicating of the collaboration process. Without the proper tools on both sides of the conversation - where previously teams could measure the audio signal path in the lab working shoulder-to-shoulder with one another via shared equipment - debugging and validating has become increasingly challenging.
  
What does ‘good’ sound like? The role of audio test in the digital era
When defining and designing products, engineers select audio targets based on context - from penny-pinched acceptability through to luxe audiophile extravagance. However, without measurement tools, ‘good’ sound is hard to quantify. More importantly, it is hard to prove. 

It is possible to build a pretty sophisticated audio device from off-the-shelf codecs, converters, amplifier ICs and other components by simply following the manufacturer’s reference designs. But it is also easy to for the resulting product to sound just ‘OK’ - with maybe mismatched gain that results in audible noise, or mistakes in the DSP algorithms resulting in channels being slightly out of phase, or a poor phase-locked loop (PLL) implementation that causes the sample rate to wander during playback. These are all problems that are extremely hard to debug simply by listening to the device - even if listening indicates that there is a problem. Test and measurement equipment is the difference between recognising that something doesn’t sound good and developing a metric that can be set as a target, tracked and when not met, systematically debugged to produce something that sounds fantastic.

The audio landscape has undeniably been transformed - from the digital takeover, to talking appliances and dispersed engineering teams. The APx516B from Audio Precision is a direct response to these shifts. Affordable, versatile and digital-ready, this hardware-based analyser unit provides a pair of analogue signal generator channels plus 2 analyser channels. What sets it apart is the digital audio interface module slot incorporated. This is compatible with a range of modules from Bluetooth and HDMI to low-level serial data protocols (like I2S and PDM). This flexibility makes it applicable for a wide variety of current and future digital audio uses. 
  
The APx516B represents not just an advancement in audio analysis technology, but a commitment to meeting the evolving needs of the audio industry. It is a tool that was forged from the challenges of a global pandemic, and designed with the future of digital audio in mind.


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