WIFI for a Stamp

[Al Skierkiewicz]

OK, here is a subject that has a lot of confusion.
The FCC is not limiting wireless mic bandwidth. There is a discussion taking place that affects wireless mic frquencies in light of the new digital changeover and the desire by the FCC to auction off some of the previously used frequencies being abandoned by the analog transmitters. The FCC has made a statement that wireless mics come under the "unlicensed transmitter" jurisdiction and some of these mic may exceed the specifications for that rule. If that is the case then there a lot of theaters and churches that may be in violation. Wireless communications, i.e. mics, intercom, and data have all used frequencies that are regulated by the FCC in this country and their counterparts in other countries. No one is sure where all this discussion will lead. Currently new wireless mics are using UHF frequencies or the 900MHz band. Mic designs use both digital and FM modes. There are some popular mics that are available now with USB outputs for use with laptop applications.
When digitizing audio, it is common to use a sampling frequency of at least twice the highest frequency of interest. CDs for instance are 44.1kHz. This pushes the envelope of the 20Hz-22kHz accepted hearing range including the needed harmonic energy for music reproduction. If you think about it, a 22kHz sine wave would have just over two samples per cycle at 44.1kHz. Without some audio black magic, the distortion on this signal when decoded back to analog would be unlistenable. Common digital recording rates are 48KHz or multiples of this frequency (96kHz and 192Khz) to achieve the most accurate reproduction. For a comparison, TV stereo audio is bandwidth limited to 15kHz so as to not interfere with the 15734Hz pilot. Various manufacturers even limit the receivers to only 12kHz to make the decoders less complex.