Skills – SYMON MUTHEMBA

Here’s How You Make Sound Decisions on Acoustics

symonmk — Wed, 06 Dec 2017 13:47:50 +0000

Pun obviously intended. The effects of sound in some industries has an important effect on the quality of work produced as well as in some key applications, especially in the field of broadcast that I currently work in. Sound is the perceived pressure produced by the propagation of energy through a medium released when matter vibrates, while acoustics is the branch of physics that deals with the production, control, transmission, reception, and effects of sound. Some of the areas of application that are dependent on sound are full/hemi anechoic chambers, radio and television studios, airports, nightclubs, torture chambers (just a guess, I’m not completely sure about this one), recording booths and many more. These are environments where sound needs to be well controlled. An example that I’ve dealt with was in radio studios. Imagine listening to your favorite radio show in the morning then you faintly hear the buzz of a helicopter or the bark of a dog within the show. Such interference would obviously dampen your experience of the show. So before you give them a bad rating, get to know what they should’ve done. Soundproofing and Isolation Soundproofing is the act of minimizing the entry of external noise into a room. Noise comes from many areas; outside noise from traffic, planes; from inside the building like chatter, walking and movement. Noise is captured by sensitive microphones typically used in these applications. It’s obvious measures have to be taken to mitigate the effects of noise in a lab or studio, since running tests or shows only at 3am, dead in the night, is not much of an option. Therefore, soundproofing isolates an area from effects of such noise For proper isolation, consider right from the very architectural plan of these rooms to cater for factors such as sound pressure, to ensure desired noise levels. The room should be ‘shielded’ from outside noise sources using several ways: Construction with heavy material such as thick concrete walls Use of double doors Heavy doors Closing off the studios from sources of noise within the building such as steps, chatter Sealing any and all air gaps on windows and doors Acoustic Treatment Acoustic treatment refers to measures taken to ensure good quality sound capture/recording within a room. In-room noise from echo, air conditioning systems and computer fans lead to poor sound capture and this can never be reduced through isolation as discussed earlier. Treating a room requires knowledge of the kind of sound to be captured but a few methods that we will discuss will greatly improve the sound quality compared to no treatment at all. When we’re discussing acoustic treatment, we refer to catering for the following scenarios: Reflection of low frequency sound off the room walls caused by the size and dimensions of the room. Reflection of mid to high frequency sound off hard surfaces within the room. To have the best sound, an investment in acoustic treatment material that absorbs and diffuses sound MUST be made. Sound absorption Sound that bounces off surfaces can be reduced by placing panels which absorb the sound before it reflects back to the capturing devices. You can easily check the acoustic properties of your room by walking to every point of the room and clapping your hands as loudly as you can. Check the reverberations that are produced, if you get audible echoes especially with a ringing sound, you need a great deal of treatment, if you have minimal reverberation, this is good though you still stand a chance to benefit from some acoustical treatment. The room can be treated using some of the following methods: Using bass traps to absorb low frequencies Using acoustic panels and foam boards to absorb the mid to high frequencies Using diffusers to scatter the other frequencies Use an acoustic carpet specially made to absorb sound In an-echoic chambers, use of large acoustic absorbers Such items could be found locally in Nairobi, like acoustic carpets are easily found at Tile & Carpet Center and other vendors of these products. Final considerations you could make are the equipment to be used in the room, like computers whose fans make noise, the air conditioning system may also bring in undesired noise. However, different people may want different noise levels in a room so plan and execute wisely with proper research and consult the experts. Fun fact: Microsoft broke the world record for constructing the quietest place ever and they have an interactive website to show you how they did it, sounds really interesting.

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Recognizing “ndiyo” and “hapana” speech using MATLAB algorithms and FFT functions

symonmk — Tue, 18 Jul 2017 14:24:00 +0000

Ndiyo means yes in Swahili and hapana means no. The two words were chosen as they can be used to make very simple applications that may require a yes/no response such as an automatic telephone prompt system. Swahili translations of yes/no applies to the national language of Kenya, and an interface that recognizes the words can be used in local applications. Simple speech recognition The first step is to obtain speech samples of ndiyo and hapana from a large sample of people throughout the country. This can be done using a simple microphone and a recording instrument. For this project however, I took the generic pronunciations of the words from Google translate: ndiyo, hapana (I know, sounds weird). We can now plot the two audio files as a periodogram Power Spectral Density plot using fast Fourier transform (FFT) in MATLAB. FFT is simply an algorithm that makes computation of discrete Fourier transforms (DFT) more efficient by reducing the amount of computations involved. OR This gives the plots in figures 1 and 2. According to the two plots above, we can see that the signal for ndiyo has more energy in the lower frequencies than that of hapana. We can use this feature to differentiate the two signals. When the signals approach 4kHz however, they exhibit features that are similar and harder to differentiate. Trial and error resulted in a range of 0 to 3620 Hz for the lower frequencies and 3620 to 11025 for the higher frequencies. A threshold value is necessary for the separation of the features, this value is obtained by calculating the feature for all of the audio samples and examining the histogram for the ndiyo and hapana values. I chose a threshold value of 12 as an example but in practice this figure should be computed. The speech recognition algorithm is: Using this algorithm, the output for the speech recognition function on the two audio files is: This shows that the algorithm exercise was successful in distinguishing the speech from two audio sources using a simple recognition algorithm. REFERENCES AND SUPPORTING ARTICLES ‘Power Spectral Density Estimates Using FFT’ https://www.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html. ‘DSP Mini-Project: An Automatic Speaker Recognition System’ http://minhdo.ece.illinois.edu/teaching/speaker_recognition/speaker_recognition.html. ‘Basic feature extraction and classification of audio files’ https://ccrma.stanford.edu/workshops/mir2011/Lab_1_2011.pdf. Enhance your DSP Course with These Interesting Projects http://www.asee.org/file_server/papers/attachment/file/0002/2611/Enhance_your_DSP_Course_with_these_Interesting_Projects.pdf.

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Ten Essential Skills for Electrical Engineers by Barry L. Dorr, Chapter 10 Part 1 Summary

symonmk — Tue, 09 May 2017 10:13:01 +0000

Ten Essential Skills for Electrical Engineers is a wonderful book and at the writing of this post I am summarizing the fifth chapter. However, I couldn’t resist skipping over to read the tenth chapter, GETTING A JOB – KEEPING A JOB – ENJOYING YOUR WORK. In this chapter, Dave a 74 year old friend of the author and successful engineer, joins in writing this chapter. Together with Dorr, they provide suggestions on getting and enjoying an engineering career in the following ways: Positively distinguishing yourself from other job applicants Distinguishing yourself in the workplace The chapter is divided into three parts: How to effectively market yourself to ccompanies as a candidate with strong technical and interpersonal skills How to quickly develop skills that will make you a valuable part of any engineering department How to ensure the nearly 100,000 hours of your working life be satisfying, rewarding and meaningful This chapter advises one to select the information that is right for you at the moment. For myself, I will focus on the first part. Part 1. Getting a Job First of all, familiarize yourself with the corporate hiring process. This is usually done in 4 steps: Step 1, Computer screening. Step 2, Review by Human Resource personnel. Step 3, Telephone screening. Step 4, Interviews at company. Tips for bypassing the above corporate hiring process: Avoid the computer screening process by taking advantage of all the job placement assistance available at your school Target companies carefully and send resumes to individuals within the company Getting an Interview Take and pass required engineering exams and certifications by these companies Get some experience, in form of internships or projects Attend job fairs Send resumes to a carefully chosen set of companies Send your resume to the right person Always accompany a resume with a cover letter Contact companies even if they are not hiring Preparing for an Interview Get your suit cleaned and pressed Prepare to discuss anything on your resume Mentally prepare to be interviewed by a team Be prepared for the interviewer to ask you to discuss a subject of your choice The Interview There might be an initial telephone screen. If you do well, you will be invited for an on site interview. At this stage, follow the following: Treat the telephone screen as you would a normal. serious interview Be prepared to work problems Be confident and enthusiastic Don’t worry about being nervous When asked something you don’t know, do not give up or panic If the interviewer is inexperienced (like in your particular expertise) help him/her out in understanding When doing problems, check your work When asked about team projects, make sire to credit your team members Be prepared to ask the interviewer questions Send a follow-up email immediately after the interview Selecting the Right Offer After going through the above stages and hopefully succeeding in getting an offer for a job, it might still be important to ask yourself these questions: Does the company offer job security? Did the company offer a high starting salary? Did you meet mentors you could learn from? Did you see women in engineering and management positions? (Relevant benefit to female candidates) Is the laboratory well equipped? The above is only a shallow summary. The complete book further elaborates each point stated. I will continuously internalize on these concepts as I continue with my studies and career search. The next two parts will become relevant to me as soon as I start working and I’ll be sure to capture that too!

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Using KiCad EDA to Build Electronic Components and Design Schematics

symonmk — Tue, 21 Mar 2017 18:23:34 +0000

KiCad is a free development software for electronic design automation (EDA) that I have been looking around into to designing my final year school project (more on that later) schematics. KiCad is extensively developed and used almost exclusively by CERN! With a lot of online documentation, support and large communities, the experience of using this software has been mostly uncomplicated and a lot of fun. Resources and Tutorials KiCad can be downloaded for free from their website Find component libraries here I used the Getting To Blinky 4.0 tutorial by Contextual Electronics. This is a popular tutorial series published by the CE guys and they’re even supportive enough to release an updated version. Useful Documentation From KiCad official documentation website. Also checkout this well written documentation from Gearbox Community Forum. I advise checking out the Splashboard V2 IoT thread on the same forum for best practices with KiCad. It is well discussed. Project In order to construct the internal schematic of the HC-12 Transceiver, I studied the datasheets of its main components: Si4463 transceiver, STM8S003F3 microcontroller and AS179-92 switch. These components were not in the component libraries linked above therefore I created a separate library to house these components and proceeded to construct the components in the Schematic Library Editor in KiCad. The above image is a split screen of the library component being created while referencing its datasheet and GTB tutorial. At the moment I’ve set up the HC-12 Transceiver as shown: *This is definitely not the final schematic and is my first major attempt. I will update with more in the near future.

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