Low Noise USB Audio Device (SAM Scribe Mk II)

Beta Solutions partnered with Atkinson & Rapley Consulting Ltd, designing a dual-channel, broad-spectrum, USB sound recording device for recording environmental sound, specifically for investigating industrial noise pollution. The low noise specifications were very strict, but the end result surpassed their expectations. 

Sam Scribe Mk II

Opportunity

Atkinson & Rapley Consulting developed the SAM Scribe Mk I device to record audio in the infrasound and audible range (0.1 - 20,000Hz). The device, launched in early 2016, enabled non-specialists to record and analyse soundscapes with laboratory-accuracy. After having success in the Australian market, Atkinson & Rapley Consulting looked to develop a second generation unit with the following requirements:

  • Designed for ease of manufacturing
  • Additional features - including advanced analogue signal switching
  • Strong bias toward "intuitive-use" (Human Factors design)
  • Ideally an increase in SNR performance 
  • Ideally lower overall cost

Atkinson & Rapley Consulting considered a few R&D consultants and in the end engaged Beta Solutions as their product innovation partner. This was primarily due to their friendly approach and proven experience in the field of audio electronic design. 

Solution

The first step was to work with Atkinson & Rapley Consulting to understand their needs and their customer requirements. It was immediately evident that the product had to incorporate a strong human factors design element. That is, it was vital that the product not only performed well, but also looked good and was as straight forward to operate as possible.

Design Phase

Once the layout and specifications were agreed, we undertook some SPICE simulations to validate the initial design calculations. As can be seen in the graph below, one requirement was that the bandpass had a low end cut off frequency of only 0.1Hz. This was somewhat challenging, as the vast majority of off-the-shelf solutions have a band pass low end cut off frequency of >10Hz. Every component in the audio path had to be capable of passing through the 0.1Hz - including the various coupling capacitors and analogue to digital circuitry.

Simulated Frequency Response

The PCB was designed using the very latest version of Altium Designer which - in addition to the standard 2D PCB layout - enabled us to create 3D models of the intended circuit board. We then used these 3D models to cross check that the PCB would meet our required clearance constraints for the intended mechanical aluminium enclosure.

PCB designed in Altium Designer

A very strong emphasis was placed on designing the circuit to minimise electrical noise from external and internal sources. This involved selecting all components (including capacitors, OpAmps, power supplies, and ADCs) correctly - carefully ensuring the components' datasheets specified the required low noise characteristics. Additionally, any "noise generating" (digital) circuitry was kept well away from any sensitive analogue audio paths, with solid PCB copper ground planes being used extensively (on multiple layers) to help shield the circuitry from unwanted conductive and radiated emissions.

Circuit designed to minimise electrical noise

 

Prototyping and Testing Phase

Once the design was completed, a prototype PCB was produced. The fully functional prototype allowed us to validate the design - ensuring it met the required specifications. Various audio tests were undertaken utilising our specialist diagnostics and test equipment - including oscilloscopes and spectrum analysers.  
Atkinson & Rapley Consulting undertook the final Acceptance Testing, and the prototype was found to have exceeded expectations - out performing their original Mk1 device by 5dB on average.

For those who are not familiar with the acoustical dB scale:

  • 140dB is a military jet taking off
  • 110dB is a typical rock concert
  • 60dB is about the level of normal conversation 
  • 20dB is whispering or leaves rustling 
  • 10dB is someone breathing
  • 0dB is the technical limit of human hearing. 

 The SAM Scribe Mk II's noise floor (in one particular mode) is less than 0dB (SPL)  between 100Hz and 1000Hz (approx). Essentially this means that electronics produce less than the signal from a microphone responding to a 20 micro-Pascal air fluctuation.

Real Time Audio Output

Production Phase

Just as with the R&D phase, Atkinson & Rapley Consulting have turned to Beta Solutions to assist them with the PCB production aspect of the project. We have been able to produce the required quantities in the shortest possible time. Like all of the products that we produce for our clients, we undertake all the required programming, assembling and testing before giving the product the "QC Sticker" stamp of approval.

QC Stickers

Success

Atkinson & Rapley Consulting are thrilled that we have been able to deliver this project on Spec, on Time and on Budget. The SAM Scribe Mk II has now completed the first commercial production run and sales continue to increase as the demand for these fantastic products rises. More information about Atkinson & Rapley Consulting's SAM Scribe product can be found on their website.

Client Testimonial

It is rare to find the combination of high-technology technical expertise, practical hands-on skills with sophisticated and friendly customer service, yet Beta Solutions has these. When we approached Beta Solutions to partner our product development, they were able to combine analog and digital design skills with a deep understanding of human interfacing that allowed them to design a stunning product from our technical brief.

Beta Solutions project management skills and communication with the client has always been superb and any problems that surfaced were dealt with quickly and efficiently, and at the lowest possible cost to the client.
 
Beta Solution’s combined talents are exemplary. That Beta Solutions have such a comprehensive team to focus on each project has meant that the overall R&D operation was smooth and effective from inception to finished product. The high-tech knowledge and state-of-the-art facilities make them a one-stop-shop for electronic product design and manufacture. Atkinson & Rapley Consulting cannot recommend them highly enough.

Dr. Bruce Rapley
Principal Consultant: Environmental Health, Acoustics and Human Cognition,
Atkinson & Rapley Consulting Ltd.

 

* All the content in this article, including imagery, has been approved by our client for publication on this website.