Everything You Need to Know About Digital Signal Processing

Digital signal processing is defined as the science of signals and systems that allows us to generate, modify, and analyze digital signals and data. It’s also a key component of the software that enables data sharing between devices using data-over-audio. In fact, digital signal processing enables countless activities, such as filtering, speech recognition, image enhancement, data compression, neural networks, and much more. More specifically, as it relates to transmitting data-over-sound, these activities include encoding data into an audio signal and decoding the data in order to extract it from the audio signal.

Putting Data into Sound

Using audio signal processing, data is added to an audio signal using software by generating and modifying a sound wave (modulation). One method used to encode data into sound is called frequency-shift keying (FSK), a simple digital modulation technique. A binary FSK signal uses two frequencies; a quadrature FSK uses four frequencies. Here at LISNR, we also use PSK, phase-shift keying. By increasing the number of frequencies used for FSK or the number of phases we use for PSK, LISNR is able to increase the number of bits sent in a certain amount of time.

Once encoded, it’s possible for data to move from one device to one or more other devices by being broadcasted by any standard speaker and received by a standard microphone. The device receiving these sounds needs a signal that indicates some data is available for delivery and translation (demodulation). For this reason it’s necessary for an audio tone to include some directions as metadata to help the receiving device understand what kind of information it will be receiving and what it should do with the data.

Extracting Data from Sound

Extracting the data (demodulation) can only occur when the receiving device identifies a data-over-audio signal. Each signal has a sequence called a “preamble” affixed to the beginning of the data packet. When the decoder hears and recognizes the correct preamble, it understands that a signal is present, and begins the demodulation process. Once the signal is verified, the decoder checks the data against the valid frequency options. If everything checks out, the data will be extracted from the audio signal, the instructions included in the data will be identified, and the secondary action will be initiated (e.g. display text, play a sound, pass information to an app).

The file size transmitted over audio is determined by the technology of each solution provider, regardless of the hardware. Transmitting that sound from one device to one or more devices requires only a speaker (to send) and a microphone (to receive). However, there are external factors that can affect the process of sending and receiving sound waves.

Overcoming Sound Barriers

The best possible ultrasonic data transmissions can be affected by the hardware and software that are transmitting data to and from and the environment these devices are in. These factors are very important in sending data using digital signal processing. Most mobile devices have adequate hardware; however, in some specific cases, speaker systems employ filters to remove near-ultrasonic and ultrasonic frequencies to improve sound quality. In these uncommon circumstances, those filters may affect ultrasonic data signals, so the filters need to be disabled.

Another common challenge is reverberation, or a series of echoes in a short period of time that are created when a sound wave bounces off something. Small spaces and lots of reflective surfaces, like concrete, glass, and many sharp angles, increase reverberation. Two ways to mitigate reverberation include sound absorbing materials (carpeting, curtains, acoustic panels), which decrease the likelihood of echoes, and filters and equalizers. Filters can be used to reduce effects like reverberation and they work in any type of modulation. Equalizers can also be used to reduce reverberation and inter-symbol interference.

LISNR’s Take on Digital Signal Processing

LISNR has created proprietary digital signal processing technologies backed by global patents dating back to 2012. We are solely focused on offering our customers a robust and simple-to-integrate platform for enabling micro-communication in payments, customer journey, and proximity marketing use cases. Further integration of our technology via our software development kit allows consumers using virtually any modern mobile device to utilize our technology to encode and decode data into audio in any environment.

Want to learn more about how digital signal processing works? Get in touch to connect with our team regarding how data-over-sound can help your business.

 

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