• b.Figure Q10b shows the output levels (in dB) from the first 8 critical sub-bands of a MP3 encoder, at two consecutive analysis frames 25ms apart:

Figure Q10b

MP3 Sub-band Number	1	2	3	4	5	6	7	8
Output Level (dB) at T1	29	58 *	12	44	63 *	21	18	4
Output Level (dB) at T1+25ms	0	8	0	0	60	0	0	0

• During the analysis at time T₁, it is found that Band #2 provides 22dB of masking to Band #1 and 16dB to Band #3, while Band #5 provides 24dB of masking to both Band #4 and Band #6.

  Determine the following:

  • i.Which of the sub-bands will need to be encoded at time T₁? Give reasons for each of the 8 sub-bands.

  (8 marks)

  • ii.For the sub-bands identified to be encoded in part i., how many bits per sample must be allocated?

  (6 marks)

  • iii.During the next critical band analysis at time T₁+25ms, it is found as shown in Figure Q10b that only Band #2 and Band #5 have non-zero outputs.

    State with reasons, whether Band #2 and Band #5 need to be encoded, and if so, how many bits per sample must be respectively allocated?

  (3 marks)