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67 lines
1.8 KiB
Python
67 lines
1.8 KiB
Python
import numpy as np
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import cmsisdsp.datatype as dt
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def frequencyToMelSpace(freq):
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return 1127.0 * np.log(1.0 + freq / 700.0)
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def melSpaceToFrequency(mels):
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return 700.0 * (np.exp(mels / 1127.0) - 1.0)
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def melFilterMatrix(dtype,fmin, fmax, numOfMelFilters,fs,FFTSize):
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filters = np.zeros((numOfMelFilters,int(FFTSize/2+1)))
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zeros = np.zeros(int(FFTSize // 2 ))
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fmin_mel = frequencyToMelSpace(fmin)
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fmax_mel = frequencyToMelSpace(fmax)
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mels = np.linspace(fmin_mel, fmax_mel, num=numOfMelFilters+2)
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linearfreqs = np.linspace( 0, fs/2.0, int(FFTSize // 2 + 1) )
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spectrogrammels = frequencyToMelSpace(linearfreqs)[1:]
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filtPos=[]
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filtLen=[]
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totalLen = 0
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packedFilters = []
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for n in range(numOfMelFilters):
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upper = (spectrogrammels - mels[n])/(mels[n+1]-mels[n])
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lower = (mels[n+2] - spectrogrammels)/(mels[n+2]-mels[n+1])
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filters[n, :] = np.hstack([0,np.maximum(zeros,np.minimum(upper,lower))])
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nb = 0
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startFound = False
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for sample in filters[n, :]:
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if not startFound and sample != 0.0:
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startFound = True
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startPos = nb
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if startFound and sample == 0.0:
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endPos = nb - 1
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break
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nb = nb + 1
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filtLen.append(endPos - startPos+1)
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totalLen += endPos - startPos + 1
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filtPos.append(startPos)
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packedFilters += list(filters[n, startPos:endPos+1])
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return filtLen,filtPos,dt.convert(packedFilters,dtype)
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def dctMatrix(dtype,numOfDctOutputs, numOfMelFilters):
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result = np.zeros((numOfDctOutputs,numOfMelFilters))
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s=(np.linspace(1,numOfMelFilters,numOfMelFilters) - 0.5)/numOfMelFilters
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for i in range(0, numOfDctOutputs):
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result[i,:]=np.cos(i * np.pi*s) * np.sqrt(2.0/numOfMelFilters)
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return dt.convert(result.reshape(numOfDctOutputs*numOfMelFilters),dtype)
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