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Solution to HW#1: Audio Processing


  • Learn audio processing, audio compression techniques, and  MP3 standard.
  • Establish CS525 personal web page. Learn how to add photo image and embed audio.
  • Assignment Date: 1/21/2010

    Due Date: Part 1: 1/27/2010; Part 2: 2/1/2010


    Related Resources and Logistics:

    Part 1:

    Part 2:

    1. Audio Encoding.
      With mono, 16 bits, 22 kHz, PCM encoding, how many bytes of data will be generated by a three minute sound recording?
      Ans: 1*16*22000*3*60 bits / 8 bits/byte = 7,920,000 bytes.
    2. Embed Audio in a Web Page.
      Use Adobe Soundbooth or any audio editor to record a less than 5 second greeting voice with mono, 16 bit, 22kHz, encoding. Edit out the unnecessary silence portion of the sound track and apply the normalized special effect. Save as .wav and .mp3 file format. scp or sftp your audio files to your public_html/cs525/audio directory and create a hyperlink in your class personal web page. Embeded it in your cs525 web page using <embed src="audio/achattop.mp3" autostart=true hidden=true loop=false></embed> Replacing achattop.mp3 with <yourlogin>.mp3.
      Question 2.2. What are size differences among audio files encoded in .wav, .mp3 and that used pcm encoding (estimated)?
      Ans: Here are the list of the audio files with different encoding formats for my web site welcome recording. MP3 compress ratio is about 4.9:1 ratio. AAC compressed ratio is about 9.1. 3GPP mobile multimedia compress ratio is about 12.2.
      Fileformat FileName Size
      PCM/Wave chowWebSiteWelcome441k.wav 292kB
      MP3 chowWebSiteWelcome441k.mp3 60kB
      QuickTime/AAC chowWebSiteWelcome441k.mov 32kB
      3GPP chowWebSiteWelcome441k.3gp 24kB
    3. MP3 Audio Masking Exercise with Matlab.
      Repeat the exercise 3
      in audio.html handout, by using 300Hz as masker (sig1). Find out the corresponding masking thresholds for the 300 Hz signal at 200Hz (sigLow) and 420Hz (sigHigh) by generating and evaluating the synthesized signals (sigA, sigB, sigC) with the following formula in Matlab code. You may adjust the signal ratio of the masked signal until you can recognize the masked signal. Save the wave files generated by this exercise in your CS525 web site, and include their urls and the masking thresholds as your submission.
      1. sigA=[sig1 sig1+0.031622777*sigLow] % sigLow is 30dB weaker
      2. sigB=[sig1 sig1+0.1*sigHigh] %sigHigh is 20dB weaker
      3. sigC=[sig1 sig1+0.1*sigLow+0.1*sigHigh]