Final Exam CS4LP Time : 1 hour 30 minutes Close books

Transcription

1 Final Exam CS4LP Time : 1 hour 30 minutes Close books 1. Briefly explain what is a physical sound and its principal characteristics. Variation of pressure propagating in space. We measure sound in decibel. A sound has a frequency and a high. 2. Give the three type of sound and a example for each one of them. Pure sound : perfect sinusoid Harmonious sound : several perfect sinusoid with different frequencies Acoustic sound : Harmonious with noise 3. With what measure do we represent a digital sound? Sampling for the time quantification for the high 4. How do we use these measure to represent a digital sound? The sampling is use as a unit of time. For each sampling we will have a quantification. Reading a sound file is so reading the quantification for each sampling. We can compare it as an array. 5. Give at least 3 characteristics that represent a digital sound. (difference between 2 representations) Integer / Floating Arithmetic Signed / unsigned numbers Encoding 8 / 16 / 24 / 32 / 64 bits Endianness 6. Give the 3 shapes of data to stock digital sound and what information we stock in each part of a shape. Data Header Data Header Meta-data Data The data include all of the data for a sound file. Header contains sampling rate, quantification, canal, size data Meta-data contains additional information as artiste, song title, album 7. How can we compress information? Give a definition of each compression and an example of file using each compression. What is the compression rate for each one of them? With or without lost of information. Without lost of information we can compress with several technique. Using Entropy compression, dictionary of values (GZIP), prediction and encoding by sequence (Golomb-Rice).The compression rate is between 30% and 60%. With lost of information, we use the limitation of human ears. Suppression scale on human ears, temporal mask (sound hide by another one), frequencies mask (frequency hide by another one). The compression rate is about 90%.

2 8. What is the MIDI? MIDI is an interface, a exchange messages protocol or a file format. It is used to describe musical event. 9. Give 3 instructions of the MIDI protocol. note ON note OFF velocity XX aftertouch XX Pitch modulation 10. How can we compress the information of the MIDI protocol? suppression of note OFF by the running status Suppression of data byte (obvious argument) 11. What is General MIDI? And what did it do? General MIDI is a norm for the MIDI. It impose minimum polyphony, minimum canal supported and velocity supported. It normalize instrument number, controller number, identification constructor. 12. Give the general structure of a midi file and give 2 example of midi file. Header Header Track Data Track Header Track Data Track Midi file :.SMF (standard midi file).mid.kar.xmi 13. Give 3 modules used in PureData. Object Message Comment Number Bang Sliders 14. Explain what does the following patch :

3 Create a Harmonious Sound. 15. Give the general structure of classes that represent MIDI in the JAVA sound API. a) 16. What does the 3 following effect? Create a real-time effect that multiply the data of a sample by g. It is the gain effect. b)

4 It's a Offline effect that create a echo. c)

5 A Offline effect that create a melted. 17. Explain what is LADSAP and what we can do with it. LADSAP is an API encoding in C for Unix computer. Its is specific for modular audio effects. By modify the file ladsap.h we can create an audio effect that you can apply through the LADSAP SDK : analyzeplugin and applyplugin. 18. Describe a LADSAP plugin. 19. Give two example of audio software. Audacity Protool 20. Explain how to apply a effect in audacity. Create a new project. Import the file you want to modify. Select with the cursor the portion of file you want to modify. Go to effect, select the effect you want. Enter the parameter needed. Click Apply.