Numpy FFT sample (4-bit digitized sin function)

fft_sample.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Maximum-power bin       : 1293\n",
      "Maximum-power frequency : 1499580.084\n"
     ]
    },
    {
     "data": {
      "image/png": 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      "text/plain": [
       "<matplotlib.figure.Figure at 0x111fa46d0>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "%matplotlib inline\n",
    "import matplotlib.pyplot as plt\n",
    "import numpy as np\n",
    "\n",
    "# Constants\n",
    "dataFile = \"sin.text\"\n",
    "samplingFreq = 5.8e6\n",
    "samplingPeriod = 1/samplingFreq\n",
    "\n",
    "# Read data\n",
    "# 数字が文字として並んだテキストファイルを読み込む。\n",
    "# sin.textは、sinを4ビットでサンプルした値が5000個並んだデータ。\n",
    "dataString = open(dataFile).read()\n",
    "n = len(dataString)\n",
    "d = np.zeros(n)\n",
    "for i in np.arange(n-1):\n",
    "    d[i]=int(dataString[i])\n",
    "\n",
    "# Subtract the DC component\n",
    "d = d - np.mean(d)\n",
    "\n",
    "# FFT - X axis\n",
    "fftfreq = np.fft.fftfreq(n, samplingPeriod)\n",
    "\n",
    "# FFT - Y axis\n",
    "fft = np.fft.fft(d)[0:n/2]\n",
    "fftmag = np.abs(fft)\n",
    "\n",
    "# FFT - Plot\n",
    "fig, panel = plt.subplots(1,1)\n",
    "panel.set_xlim(0, fftfreq[:len(fftmag)][-1])\n",
    "# panel.set_ylim(1e-1,1e4)\n",
    "# panel.set_yscale(\"log\")\n",
    "panel.plot(fftfreq[:len(fftmag)], fftmag)\n",
    "\n",
    "# Save figure\n",
    "fig.savefig(\"fft_sample.png\", dpi=200)\n",
    "\n",
    "# Maximum power bin and frequency\n",
    "binIndexMaxPower = np.argmax(fftmag)\n",
    "freqResolution = samplingFreq / n\n",
    "freqMaxPower = binIndexMaxPower*freqResolution\n",
    "print \"Maximum-power bin       : {:d}\".format(binIndexMaxPower)\n",
    "print \"Maximum-power frequency : {:.3f}\".format(freqMaxPower)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
 ],
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sin.text

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