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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

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
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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
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what school?
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anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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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.
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Damian Reply
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s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
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?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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 ?
What is lattice structure?
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
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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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