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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

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
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s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
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I'm interested in nanotube
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Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Harmonizing guitar pre-amp. OpenStax CNX. Dec 15, 2015 Download for free at http://legacy.cnx.org/content/col11932/1.4
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