Physics is True
Posted on January 15, 2012
Yesterday I tinkered with increased bit-rate streaming, stepping up from 24kbps all the way to 40kbps, following Artisan Radio’s report that there is a detectable improvement even compared to 32kbps, which I also tried.
The stream sounded better.
Using Hans van Zutphen’s Stereo Tool for processing, I set the bandpass filter to a range of 40 to 20,000 Hz for the following reasons:
Using an article by Dave Moulten from TV Technology titled Thinking About Equalization: The Audio, I set the low end at 40 Hz because Mr. Moulten reports that the 1st octave of the audio spectrum, 20 to 40 Hz, contains little musical content and is not reproduced by most loudspeakers, so I turned it off;
Next the Nyquist Theorem applied (is that right), in which actual frequency response is 50% of the bandwidth. Therefore, at 40kbps the 50% frequency would be 20kHz. True?
The next day I got to thinking about the AM transmission, with bandwidth typically limited to the carrier width, residing on a 10kHz channel. To observe the modulation result using the upper audio band to 20kHz, I tuned to the channel adjacent to 1680kHz, namely 1670kHz, and noted active splash on sibilant sounds and piccolo notes.
SO I set the Stereo Tool bandwidth to a top limit of 5kHz and the modulation spillover at 1670kHz disappeared.
Always the quandry, that means either the stream would best match the situation by tuning down to, say, 16kbs, or…. I guess an outboard component bandpass filter for the transmitter would permit optimizing both types of transmission….
Join us again tomorrow.