# 8.4 Analyzing the signal

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This module discuss the process of analyzing an audio signal for music transcription.

## Distinguishing between notes

Our second module (get_note) is the one that will analyze the signal at a specific time, split the signal into the different notes, and get the frequencies of each note. Since each element of the matrix corresponds to a magnitude, the frequency with the maximum magnitude at a specific time instant represents the frequency of the signal at that time. Therefore, we need to check the maximum magnitude for every column and determine the frequency. Sometimes, however, some columns will not have a frequency because no note is being played ag that time instant, but it will still have a maximum magnitude at a frequency because it has noise. To deal with this, we have set a threshold magnitude that determines whether a column has a note to be analyzed or not. If the maximum magnitude at a column is below the threshold, the frequency at that time will not be considered a note, therefore it will not be analyzed.

To identify a note, we use simple edge detectors. When the signal changes frequency, the program will analyze each column until it detects another change in frequency. The range of time instants obtained from this process will represent a single note, and the frequency of the note will be the average of the maximum amplitude frequencies of each time instant in the given range. Each frequency of each note will be inputted to the identify_note module one at a time for it to output the note name. To prevent any imperfections, we have also created a time threshold, such that, if the length of a note (time instants between edge detections) is lower, such note will not be analyzed because it will not be considered a note.

NOTE: The frequency and duration thresholds work together to distinguish between notes and noise. There may be a few consecutive time instants for which noise is greater that the amplitude threshold. However, no signal should have noise that is consistently greater than the amplitude threshold for the duration of the duration threshold or longer. As such the two thresholds work in tandem to eliminate notes from the transcription process.

NOTE: The duration threshold does involve a tradeoff: while noise is eliminated, the user is prevented from analyzing a file that contains notes that are less than 100 time instants long. Any such note would be treated as noise. As such, the program may be unable to correctly handle very fast rhythms in low quality signals.

## Identifying notes

Our next module will basically identify the note. It takes a frequency as an input and it outputs a string with the name of the note being played. We have created a library with different frequency ranges that correspond to different notes. The module will find the range to which the input frequency corresponds and input output the string for that range. This process will be done for every note that is given by the get_note module.

This identification process would not be possible if we only had a regular spectrogram, since the precision is very low, causing a very high error that would lead to wrong identification of a note. The frequency reassignment process is an extremely essential part of this method.

## Generating synthetic audio files

As an extra module, we have created a simple function to create tones, in order to test our project. In this function, we have different square waves with different frequencies. We simply create a vector with the notes that we want and we have a song to be analyzed.

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
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NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
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what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
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