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The solution we came up with to alleviate this problem is to average what the program thinks is the highest frequencies across multiple frames of data. We tested out different average lengths and found that averaging every 25 frames sounded the best. Our code will keep track of a variable-length list that contains the frequency of the highest peak per frame. At the start of every frame a new frequency value will be added to the list, and at the end of every frame the list is averaged to determine a single frequency. This list resets every 25 frames. In midst of this process, we also converted to linear frequency from FFT bins, which is done by multiplying by the ratio of the sampling frequency over half the chunk length. To further improve our results, we only added to the list frequencies if the magnitude of that particular frequency bin is above a particular value. This way our code will ignore the low amplitude noise and only record frequencies when a note is being played.

flag = 0 freq = []while(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) highest_freq = numpy.argmax(abs(X[0:511]))flag +=1 if (X[highest_freq]>5000): freq.append(highest_freq*44100/(CHUNK/2))avg = (sum(freq)/len(freq)) if flag == 25:flag = 0freq = []

Creating the harmony

Once we have the correct frequency and the identity of the note, we proceed to figure out the frequency of the harmonizing note. We first create a Python dictionary of musical keys mapped to a list of the corresponding frequencies of that note at different octaves. For purposes of demonstration, we only added the key of C to the dictionary. However, other keys could easily be added. We then created a function that helps on determine which harmonic we are in given a musical key and the frequency of a note. We then apply the formula for finding the harmonizing frequencies describe in the previous section to the frequency we have and obtain the frequency of the third and fifth intervals from the note being played.

keys = {'c':[1636,1636/2,1636/4,1636/8]}sBuf = 50 def key_select(freq, key):for f in keys[key]:if freq>= f: return freturn freq def chord_freqs(key, note):n = 1200*numpy.log2(note/key) if(500-sBuf<= n<=500+sBuf or 700-sBuf<= n<=700+sBuf or n<=sBuf): f3 = note * math.pow(2, (400)/1200)f5 = note * math.pow(2, (700)/1200) return f3 , f5elif (200-sBuf<n<200+sBuf or 400-sBuf<n<400+sBuf or 900-sBuf<n<900+sBuf): f3 = note * math.pow(2, (300)/1200)f5 = note * math.pow(2, (700)/1200) return f3, f5elif (1100-sBuf<n<1100+sBuf): f3 = note * math.pow(2, (300)/1200)f5 = note * math.pow(2, (600)/1200) return f3, f5else: return 0,0

After obtaining the two harmony frequencies, we tried to take them into the time domain. We initially tried add triangles of frequency content centered at the desired frequencies and then taking the inverse transform, in hope to try to mimic a "real" sound. However, doing that caused the note to sound slightly off. Also we didn't add imaginary components to the frequency and the FFT library gave us warnings. So we decided to try out other approaches. The next thing we thought of was using the Karplus-Strong Plucked String algorithm to create a realistic decaying note. But we very quickly saw that the algorithm was not really meant to be used in real time. The algorithm works by creating the complete decaying signal. However, this is problem with other stream because we can only output 1024 samples at a time, which is not long enough to squeeze the whole decay in. We thought about storing the whole signal from the Plucked String algorithm and output it a frame at a time. But doing so not only slow down our system, but also would introduce problems if we played a different note half way through a output decaying note. We ended up deciding to just output pure sine waves and worry about making it sound less synthesized in the future.

def play_tone(stream, frequency=252, length=1, rate=44100): chunks = []f3 , f5 = chord_freqs(key_select(frequency, 'c'), frequency) chunks.append(sine(f3, length, rate)+sine(f5, length, rate))chunk = numpy.concatenate(chunks) * 0.25 stream.write(chunk.astype(numpy.float32).tostring(), CHUNK)def sine(frequency, length, rate): length = int(length * rate)factor = float(frequency) * (numpy.pi * 2) / rate return numpy.sin(numpy.arange(length) * factor)

Now that we were only outputting pure sine waves, we decided that it would be faster and save computation complexity but just creating the sine waves of the correct frequencies in the time domain directly. This would save computation time as now we don't need to compute an inverse FFT. To put it all together. We output the harmonies through the PyAudio stream. The UCA222 takes this and adds it to the guitar signal that it is already forwarding to the speakers.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
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 .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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.
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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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