Sonntag, 20. März 2011

EE4209/EE5809 Digital Audio Processing

EE4209/EE5809 Digital Audio Processing Tutorial 3

1. MPEG-4 AAC codec is an improved version of the MPEG-2 AAC codec. The major
improvements are the inclusion of a Perceptual Noise Substitution (PNS) module and a Long-Term Prediction ( LTP) module.

Explain the principle of these modules and why are they important for allowing MPEG-4 coding of 48 kHz audio signals at 64 kbps?

2. Do a survey on the MPEG-4 general audio coding tools, and explain how various MPEG-4 audio coding tools can be used to cover applications with bit rates as low as 2 kbps and as high as 64 kbps. MPEG-4 standard also puts emphasis on scalable audio coding, explain why?

3. Summarize the specifications of DVD-Audio and Super Audio CD (SACD), and compare their advantages in terms of audio coding methods used.

4. Explain the principle of Meridian Lossless Packing (MLP) for coding of audio signals for DVD-Audio. The lossless matrix and lossless decorrelator are important ingredient to achieve the necessary coding gain for the entropy coder, explain why?

5. In FM synthesis of music, the harmonic ratio H = f m / f c is an important controlling parameter for tuning the number of harmonics generated. If the ratio is a ratio of integers, harmonic spectrum is generated, otherwise noise spectrum is generated.

Use an example of harmonic ratio of 0.25, draw the corresponding harmonic spectrum, you should indicate the positions of harmonics and magnitudes with respect to the carrier frequency.

6. In wavetable synthesis of music signals, explain the mechanism for dynamically changing the waveshape to produce quasi-periodic musical notes and the way a set of wavetables are mixed.

7. MIDI protocol for musical instruments is efficient in representing musical information, however, its sound output is synthesizer dependent, explain this statement.

8. Why is it important to calculate the reverberation time for room acoustics?

9. Explain some of the important effects on human binaural perception. How would these perceptual effects influence the design of surround sound system?

10. Describe the principles of Dolby ProLogic system for converting multichannel surround sound to a two-channel stereo sound and vice versa. Explain in particular the concept of directional enhancement.

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