This is an “open book’” exam. Please return your answer via email. For HTML / JavaScript files, either provide URLs to your files or send as attachments to the email.

1. Approximately how many bytes are required to store two channels of 10 minutes of 16-bit 44.1kHz CD-quality audio? (1 point)
   • 2 (bytes) x 44100 x 2 (stereo) x 60 x 10 ~= 100MB
2. Approximately how many operations are needed to FFT one channels of one second of 44.1kHz audio? (1 point)
   • N * Log(N): 44100 * log (44100) ~= 200,000
3. What is the order of MFLOPS does a current browser on a laptop run at? (1 point)
   • 100 MFLOPS
4. Slow moving amplitude modulation is also known as? (1 point)
   • Tremolo
5. How would you test your Web Audio application (written in JavaScript) on a Chrome browser running on an Android OS? (1 point)
   • Use aan Android emulator such as Genymotion
6. What was the name of the audio API, which was used in Firefox before Web Audio API? (1 point)
   • Audio Data API
7. What is the old name for createScriptProcessor()? (1 point)
   • createJavaScriptNode()
8. How many types of filters are available through the biquad filter in Web Audio API? (1 point)
   • lowpass, highpass, bandpass, lowshelf, highshelf, peaking, notch, and allpass
9. What is the main difference in the frequency-domain output of the ring modulation and the amplitude modulation? (1 point)
   • The center (carrier) freqiency is missing in the ring modualtion./li>
10. What is the name of the commercially successfully synthesizer that made FM synthesis popular? (1 point)
    • Yamaha DX7
11. What is wrong with the white-noise generator proposed at the end of this article? Explain. https://medium.com/web-audio/61a836e28b42 (2 points)
    • It won't sound like white-noise; because the buffer is too short.
12. Approximately how much can we compress audio signals without losing any information? (1 point)
    • about a half.
13. Fix FMbroken.html so that a) the Depth changes (via holding down the shift key);
    • Replace (line 37): osc.gain.value = e.clientY / h * 1000; with depth.gain.value = e.clientY / h * 1000;
    b) the sound doesn’t click when the mouse moves in and out of the window (Hint: one way is to create a master gain and use an envelope with setTargetAtTime() ) (Don't do this in Firefox) (3 points)
    • Replace (line 47): osc.disconnect(context.destination); with master.gain.setTargetAtTime(0, context.currentTime, 0.01);
    • Replace (line 34): osc.connect(context.destination); with master.gain.setTargetAtTime(1, context.currentTime, 0.01);
    • Replace (line 23): osc.connect(context.destination); with master.connect(context.destination); osc.connect(master);
14. Fix the following web page so that it’ll work in Firefox: http://dl.dropboxusercontent.com/u/695740/webaudiofmsynth/index.html (Just make sure that it makes sounds) (4 points)
    • main.js (line 1): var ctx = new (window.AudioContext || window.webkitAudioContext) ();
    • main.js (line 4): var mainGain = ctx.createGain();
    • fmsynth.js (line 71): this.mainGain = actx.createGain();
    • fmsynth.js (line 104): this.gain[i] = actx.createGain();
    • fmsynth.js (line 125-128): this.osc[3].start(3);etc.
    • fmsynth.js (line 198): that.osc[i].stop(0);
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Created: 2014.02.24 Modified: Ichiro Fujinaga