5 Common Mistakes in Designing Audio Signal Chains


These five common issues in signal chain designs in cost-sensitive audio solutions, if addressed, will make everything work together as a balancing act.

There is a growing demand for audio in almost everything these days as it has become the preferred interface for communication and education. With that comes the demand for high quality sound. When creating the optimal signal chain design, there are do’s and don’ts that are often overlooked. Avoiding these mistakes means saving costs. As Director of Engineering for HARMAN Embedded Audio, I lead our division of HARMAN in embedded technology hardware, software, product design, and co-branding. We’ve worked with hundreds of companies to develop the perfect audio signature for their products, whether existing or new. With cost sensitivities more critical than ever in these turbulent economic times, these solutions may be worth considering.

Mistake #1: Starting without a targeted goal

One of the first mistakes many developers make in signal chain design is not having a focused goal from the start. They may know they want audio for speakers or headphones, but audio can be customized to achieve many different results. Ask yourself, are you looking for crisp music, clear phone calls, or something else? The design of the signal chain should be specific to the intended use case. Having a lens in mind is not only important for creating the best sound for each particular lens, but it also saves money. As there are endless paths one can take to reach any stated goal, knowing your destination allows you to build the right rudder to navigate along the best and most efficient path. Design goals can be lowest cost meeting a specification, highest performance in a given 3D space, or design for a harsh environment.

Mistake #2: Not determining what is important for the specific use case

While there are many considerations to make in signal chain design, it is crucial to identify the features that are most important for the intended use case. You will want to create the feed with the correct characteristics for the chosen product or intended use. The features you can get with headphones won’t be the same as those required in a smartphone, sofa, or stadium speakers. What should you focus on in this particular project when designing your signal chain? Consider the following for example:

  • Overall frequency response: a flat or balanced frequency response is best in products like headphones, but in open spaces more bass will be needed
  • Overall sound level: the system must achieve a sound level to provide visceral sensation (stage) or the appropriate sound level to improve intelligibility (phone or headset)
  • Environment: Adding environmental noise will need to be considered as it will obscure parts of your intended audio broadcast. Are there any regulations? Stages must reach certain volumes, while headphones cannot exceed certain output levels for hearing health reasons.
  • Distortion: In most cases, lower distortion is better because it can mask or change the perception of the audio. In some cases, distortion can be an advantage to the output since most untrained listeners perceive some distortion as an overall loudness.

Mistake #3: Underestimating hardware capabilities

Hardware can be a major cost sensitivity; however, existing hardware does not completely limit the ability to add or enhance audio. If there’s no budget to replace the hardware or there’s no space left to build on, we need to strategically be able to make it work. Using software is a great method to improve the sound quality of already completed material. Several television manufacturers have come to us to improve the sound of their products. We were able to take the product and hardware they already had and implement our in-house developed software package that runs on the main processor to accomplish this without having to start from scratch or design new hardware.

This ability to add software is a powerful tool. In some cases, software is assumed to be an easy fix after the fact, but that’s not always the case. If we start at the beginning, we can design and build software and hardware in tandem, thinking about capabilities and constraints as we go. When collaborating alongside Kohler to design their Moxie showerhead speaker, we had a blank slate to work from. This meant that we were able to create the perfect mix of hardware and software which resulted in the best end product. Working together through this tends to be the most cost effective option.

Mistake #4: Not Ensuring Component Capabilities Match

It is imperative to consider the capabilities and constraints of the components. The signal chain is only as strong as its weakest link, so in the design you want to match the capabilities of the components. Once you’ve resolved this issue, you can review specific tools you can use to move toward your stated goals. For example, a smart amp can process internally. If an amp is not “smart”, you must configure it separately. What components will you need to do this?

Knowing and having the right tools is important, and this may be driven by cost. Lay out a simple storyboard to show how the signal chain moves through the product. This is where it gets tricky because most modern devices have multiple paths to go through, so they might have similar results but in the end the sounds aren’t the same. For example, if you switch from your Apple TV to your DVD player, you may get a different audio output. When doing these block diagrams, it is important that you examine each input and calculate the gains to determine how much softer or louder each block is. You will also need a suitable algorithm in each block as these can change the signal level from one to another.

As complicated as it may seem, you don’t want to make it too complex. The MIPS processor and memory are so cheap that we tend to lean on it like a crutch. With so many tools used, at some point it hits a threshold; getting caught up in using too many tools can also be a problem. Mitigate this by getting a good baseline measurement without treatment. At this point, you can consult the toolkit to determine which algorithms are best for each block. Sometimes you’ll use the same tools, sometimes they’ll be different, but use a gentle touch to make sure they work together and not apart. Too many cooks in the kitchen are not only noisy but can ruin the meal.

Mistake #5: Forgetting to Address Earnings in the System

Considering the gains of the system as a whole, there must be consistency between the signal chains. Blocks are not super devices that accept any signal and output it – they are electronically or mathematically limited. If there is too much gain, it may be too noisy. If it is too high at any stage, there will be clipping in the system which will not allow the signal to rise high enough. Work with one block at a time. It is also crucial that you listen throughout the process and that others listen to you. As acoustic engineers, it’s easy to miss things because of listening fatigue. Another’s ear can hear what you don’t hear.

Find the right solution

These five common issues in signal chain designs in cost-sensitive audio solutions, if addressed, will make everything work together as a balancing act. There are many ways to work to reduce costs. For example, the use of HARMAN Embedded’s suite of AudioEFX post-processing algorithms enables seamless mixing of hardware and software. Each block can then be tailored to each specific device, use case, and environment. This tailored approach can address all of the above factors along the way, which means avoiding any mistakes that will lead to backtracking to fit. Whichever path you choose to take, keep your ultimate goal in mind every step of the way.

Bruce Ryan is the Director of Engineering for the HARMAN Integrated Audio group based in Northridge, California and Shenzhen, China. He holds a master’s degree in engineering sciences and a master’s degree in business administration. Bruce has been with HARMAN for 20 years. His experience spans acoustics, electronics, mechanical and industrial design in automotive and consumer electronics. He currently leads the HARMAN design and development group dedicated to high-performance, cost-effective audio capture and rendering.

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