How to decrease the scale of a matplotlib spectrogram in python3

Question

I am analyzing the spectrogram's of .wav files. But after getting the code to finally work, I've run into a small issue. After saving the spectrograms of 700+ .wav files I realize that they all essentially look the same!!! This is not because they are the same audio file, but because I don't know how to change the scale of the plot to be smaller(so I can make out the differences).

I've already tried to fix this issue by looking at this StackOverflow post Changing plot scale by a factor in matplotlib

I'll show the graph of two different .wav files below

This is .wav #1

This is .wav #2

Believe it or not, these are two different .wav files, but they look super similar. And a computer especially won't be able to pick up the differences in these two .wav files if the scale is this broad.

My code is below

def individualWavToSpectrogram(myAudio, fileNameToSaveTo):
print(myAudio)
#Read file and get sampling freq [ usually 44100 Hz ]  and sound object
samplingFreq, mySound = wavfile.read(myAudio)

#Check if wave file is 16bit or 32 bit. 24bit is not supported
mySoundDataType = mySound.dtype

#We can convert our sound array to floating point values ranging from -1 to 1 as follows

mySound = mySound / (2.**15)

#Check sample points and sound channel for duel channel(5060, 2) or  (5060, ) for mono channel

mySoundShape = mySound.shape
samplePoints = float(mySound.shape[0])

#Get duration of sound file
signalDuration =  mySound.shape[0] / samplingFreq

#If two channels, then select only one channel
#mySoundOneChannel = mySound[:,0]

#if one channel then index like a 1d array, if 2 channel index into 2 dimensional array
if len(mySound.shape) > 1:
    mySoundOneChannel = mySound[:,0]
else:
    mySoundOneChannel = mySound

#Plotting the tone

# We can represent sound by plotting the pressure values against time axis.
#Create an array of sample point in one dimension
timeArray = numpy.arange(0, samplePoints, 1)

#
timeArray = timeArray / samplingFreq

#Scale to milliSeconds
timeArray = timeArray * 1000

plt.rcParams['agg.path.chunksize'] = 100000


#Plot the tone
plt.plot(timeArray, mySoundOneChannel, color='Black')
#plt.xlabel('Time (ms)')
#plt.ylabel('Amplitude')
print("trying to save")
plt.savefig('/Users/BillyBobJoe/Desktop/' + fileNameToSaveTo + '.jpg')
print("saved")
#plt.show()
#plt.close()

How can I modify this code to increase the sensitivity of the graphing so that the differences between two .wav files is made more distinct?

Thanks!

[UPDATE] I have tried using
plt.xlim((0, 16000))

But this just adds whitespace to the right of the graph like

I need a way to change the scale of each unit. so that the graph is filled out when I change the x axis from 0 - 16000

It's not entirely clear what you are trying to achieve here. If you want to zoom in, you may increase the scale, like @Nipun's anwer suggests. If you want to keep the scale but increase resolution, you may use a larger plot size, e.g. plt.rcParams['figure.figsize'] = 15, 5. — ImportanceOfBeingErnest
– ImportanceOfBeingErnest, Commented Jul 10, 2017 at 8:31
When I used the code plt.rcParams['figure.figsize'] = 15, 5 . The output image looked exactly the same — Sreehari R
– Sreehari R, Commented Jul 10, 2017 at 16:13
I highly doubt that; it would be almost 3 times larger in width direction. — ImportanceOfBeingErnest
– ImportanceOfBeingErnest, Commented Jul 10, 2017 at 18:58
I got it working now with the command plt.figure(figsize=(35,15)) — Sreehari R
– Sreehari R, Commented Jul 10, 2017 at 19:13

Nipun Batra · Accepted Answer · 2017-07-10 07:37:19Z

2

If the question is: how to limit the scale on the xaxis, say to between 0 and 1000, you can do as follows:

plt.xlim((0, 1000))

answered Jul 10, 2017 at 7:37

Nipun Batra

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5 Comments

Sreehari R Over a year ago

Can I do the same thing with the y-axis with the command plt.ylim((-1,0)) to scale the y-axis from -1 to 0?

Sreehari R Over a year ago

This just expands the graph leaving a lot of whitespaces. I need a way to change the scale of each unit. For example 1 grid space = like 0.1

ImportanceOfBeingErnest Over a year ago

@sreehari This answer tells you to use a lower value for the right axis limit (1000 instead of 8000). If you increase the limit, there is of course some whitespace left.

Sreehari R Over a year ago

The issue with doing that is that while I get the fine details from 0 - 1000, I lose all of the data from 1000-8000.

Nipun Batra Over a year ago

@sreeharirammohan : Maybe a good time to learn more about matplotlib, then. You don't lose the data, just that you don't see it in the current plot. I'd suggest using subplots with different frequency ranges.

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