<< Chapter < Page Chapter >> Page >

High level design

The high level design of our project is as follows. We have a Behringer UCA222 that serves as the interface between the pickup in the guitar and the computer. The final output is played on the speaker that is connected to the UCA via a 3.5mm audio jack. The UCA222 takes the guitar input through dual channel RCA ports and forwards the signal to the computer through USB. We then do computation and analysis, in Python, on the sample signal to determine the frequency and the identity of the note being played, and depending on the note synthesis the correct harmony. The synthesized signal is fed back into the UCA222 and outputted on the speaker.

A Block Diagram representation of our system.

Figure 1: Block Diagram of our System

A picture of our project setup.

Figure 2: Picture of our Setup

Sampling and frequency analysis

We sampled the analog signal of the pickup through the UCA222. The UCA222 is programmed to anti-alias and sample and forward the data into system audio. We can then access system audio via a Python library called PyAudio. PyAudio is able to give us vectors of the samples of a desired length. Compared the difference in latency to our system between different vector length and decide that 1024 was a good middle ground. We decided to further lowpass filter the sampled chunks to reduce high frequency noise introduced by the ‘fret-buzz’ and the initial attack of the guitar string.

import numpy import pyaudioimport scipy import math# constants fs = 44100.0CHUNK = 1024 cutoff_hz = 8000.0nyq_rate = fs / 2. # for normalizing width = 1000.0/nyq_rateripple_db = 30.0 # open pyaudio streamp = pyaudio.PyAudio() stream = p.open(format=pyaudio.paFloat32,channels=1, rate=44100, input=True,output=True, frames_per_buffer=CHUNK)# build filter N, beta = scipy.signal.kaiserord(ripple_db, width)taps = scipy.signal.firwin(N, cutoff_hz/nyq_rate, window=('kaiser', beta)) delay = 0.5 * (N-1) / fswhile(True): data = stream.read(CHUNK)x = numpy.fromstring(data, dtype=numpy.float32) x_filtered = scipy.signal.lfilter(taps, 1.0, x)X = numpy.fft.fft(x_filtered) stream.close()p.terminate()

From this, we are able to analysis each frame of 1024 samples and compute the frequency content of the frames. We played a few different notes and plotted the frequency content of notes in hopes of figuring out a good way to differentiate between notes. Below are plots of a note being struck in the time domain, and frequency spectrum plots of a high and low C note.

Time Domain plot of a note being played

Figure 3: Time Domain Plot of a note being played

Frequency spectrum of different C notes

Figure 4: Frequency Spectrum of a High and Low C

Note identification

After looking at the frequency domain, it is obvious that each note has one distinct peak at a particular frequency. So we decided to do note detection by finding the frequency with the largest magnitude. In other words, we are doing max-peak detection. In doing this, we took the absolute value of the frequency bins in the positive half of the spectrum and use the argmax function from the NumPy library obtain the frequency bin with the highest peak. However, in using this method we very quickly encountered a problem. When a certain note is played on the guitar, though the profile of the note in the frequency domain will not change very much, the maximum peak in fact moves around a little. Because other approach only looks at the highest peak, sometimes we will get errors when the neighboring peaks overtake the correct main peak in magnitude. When this happens our program will think the note is quickly changing, but actually it is just the same note reverberating through the guitar.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Berger describes sociologists as concerned with
Mueller Reply
what is hormones?
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Harmonizing guitar pre-amp. OpenStax CNX. Dec 15, 2015 Download for free at http://legacy.cnx.org/content/col11932/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Harmonizing guitar pre-amp' conversation and receive update notifications?