Project Overview

This section contains a detailed documentation of various project milestones that show the progression of the design. The documentation is structured as descriptions of the process leading to the achivement of each milestone. These accounts include references to topics that are further expanded upon in the knowledge base. Due to the nature of the content in this section, the accounts are structured as first-person reports.

Setting the goal

As with many design project, a designer is tasked with understanding a context of use and figuring out ways to alleviate any problems. In this case, the goal was well defined before the design process even began: designing a low-cost, high performance microphone preamplifier to be used for soil ecoacoustic reasearch.

Design methodology

Given my minimal experience building circuits (I had built only simple circuits to use sensors with Arduino), I chose to approach the task with curiosity and a specific design approach that was proven fruitful in previous projects. Material exploration is a methodology whereby which a designer explores the qualities of a material to discover its potentials and limits, all with the intention of understanding the practical applications it enables (Fernaeus & Sundström, 2012).

This methodology involves learning by doing. In addition, this approach recognizes that certain materials can only be understood properly while experiencing them. In this context, the material is to be understood as sound itself. Withouth previuous knowledge of audio circuitry, it can be hard to understand how components shape and manipulate sound.

Choosing the design reference

One of the early discussions between my supervisor and I was about what we should benchmark our design against. Researchers in the field use a variety of devices to acquire high quality recordings onf the nevironment. And while there are a lot of high performance preamps to choose from, there is one that is used by many researchers: the Sound Devices Mix-Pre 6. Among the impressive specs, these were the ones that interested us:

• 32bit floating point precision;
• 192 kHz sample rate;
• 142 dB of dynamic range;
• A-weighted, gain=10 dB, fader=0 dB;
• Mic Gain: +6dB to +76 dB;
• THD + Noise: 0.005% max (@1 kHz, 22-22 kHz BW, gain=20 dB, -10 dBu in)

Related works

AudioMoth

AudioMoth is a full spectrum logger whose BOM for one unit was around 53 USD in 2019 (Hill et al., 2019, p.10). It is optimised for acoustic measurements of sounds that travel through the atmosphere and comes with a built-in microphone. Extension pads for a 3,5mm jack input are provided.

ThatMicPre

ThatMicrPre is an open source microphone preamplifier with XLR input and switched gain. It has excellent noise performance and it can achieve up to 60 dB in gain. However, it requires a 48V DC power supply for phantom power.

CP5 Colour Mic Preamp

The CP5 Colour Mic Preamp by DIY Recording Equipment can achieve gain of up to 66 dB all while mantaining a good noise performance. The CP5 can be bought for around 200 USD and is designed to be mounted in a rack.

Documenting the process

This knowledge base is an edited version of the daily journaling done in the few months leading to this. The journal consisted of daily entries of varying lenght where text, pictures and drawings are used to document progress and reflect on the work. Journaling was used to critically reflect on the work and to avoid falling into rabbit holes that would lead nowhere. While the original journal remains private, this version includes everything that was learned and reflected upon during the proces.

Prototype naming

One part of meaningfully documenting work involves naming the prototypes in a way to keep track of the work and to put them into context with one another. The naming convention we eneded up adopting works as follows:

• two digits for the year of production;
• one letter for the month (from A to L);
• two digits for the day of the month;
• two digits for major architecture changes;
• two digits for iterations on the same architecture;
• a letter for small bug fixes;

The first part of the name helps to keep track progress. It also helps me track down when specific portotypes were built. The second part of the name is the one that provides context. Without it, it could get complicated to determine what each prototypes builds upon.

References

• Fernaeus, Y., & Sundström, P. (2012). The material move. How materials matter in interaction design research. Proceedings of the Designing Interactive Systems Conference, 486–495. https://doi.org/10.1145/2317956.2318029
• Hill, A. P., Prince, P., Snaddon, J. L., Doncaster, C. P., & Rogers, A. (2019). AudioMoth: A low-cost acoustic device for monitoring biodiversity and the environment. HardwareX, 6, e00073. https://doi.org/10.1016/j.ohx.2019.e00073