EE 445S Real-Time Digital Signal Processing Laboratory - Lecture 8

Before Lecture

• "Carmina Burana", UC Davis University Chorus, Alumni Chorus, Symphony Orchestra, and the Pacific Boychoir, June 2007.

• "I Feel Good", James Brown. 1950's Version.
  From the opening of Chapter 6 in an earlier edition of the Johnson, Sethares and Klein textbook: "The James Brown canon represents a vast catalogue of recordings-- the mother lode of beats-- a righteously funky legacy of grooves for us to soak in, sample, and quote." John Ballon in MustHear Review, http://www.musthear.com/reviews/funkypeople.html.

• Keeping the Peace: Round one of trying to establish a new city noise ordinance for Austin music", Andy Langer, The Austin Chronicle, Austin, Texas, May 3, 2002.
  • "downtown residents and hotels upset with noise disruptions from live music"
  • "April 17 unveiling of an amendment to Austin's amplified sound ordinance that would have reduced the legal definition of 'noise' from 85 decibels to 75dB."
  • "It's like trying to sell your house for $100,000 knowing you'll get $90,000. We were trying to get the best we could for the residents and the hotel businesses knowing we'd have to do some negotiating." From the author of the proposed change.
  In local TV news reports, proponents of new measure said that reducing noise levels from 85 dB to 75 dB at the boundary of a property was a very mild 10% reduction in noise levels. Oops!
  • "Every 10 decibels doubles the volume. Therefore, 85dB is not slightly louder than 75dB, it's twice the volume."
  The proposed change was defeated.

Announcements

• Example tradeoffs in sampling rate and amplitude resolution for analog-to-digital converters a.k.a. digitizers:
  NI PXIe-5186: two channels, 8 bits/sample, 12.5 GS/s sampling rate, 5 GHz bandwidth (Mar. 2011)
  NI PXI-5154: two channels, 8 bits/sample, 2 GS/s sampling rate, 1 GHz bandwidth
  NI PXIe-5122: 14 bits/sample, 100 MS/s sampling rate
  NI PXI-5192: 16 bits/sample, 15 MS/s sampling rate
  NI PXI-5192: 24 bits/sample, 500 kS/s sampling rate

Lecture

• Lecture on Quantization in PowerPoint format. Video: Part 1 - Part 2

Supplemental Information

• Mark A. Castellano, Todd Hiers, and Rebecca Ma, "TMS320C6000 mu-Law and A-Law Companding with Software or the McBSP", Texas Instruments Application Report, SPRA634, April 2000.
• The lecture discusses mu-law companding used in the US and Japan (u = 255) and A-law companding in Europe (A = 87.6). In the companding formulas, the log is the natural logarithm.
• A student asked what happens when a call is placed from the US to Europe. Companding in telephony is to eight bits, with one bit for the sign. Hence, the formulas in terms of |x| in [0, 1] would be used to generate a seven-bit number. To the precision of seven bits, there is no difference between A-law companding (A = 87.6) and mu-law companding (u = 255) for |x| in [0.18, 1].
• There is a mu-law pulse coded modulation (PCM) audio format. The format is an eight-bit floating-point format: 1 bit for the sign, 4 bits for the mantissa, and 3 bits for the exponent. This was a common audio format on Sun workstations.

Last updated 09/20/14. Send comments to bevans@ece.utexas.edu