On Wed,11/9/2016 9:21 PM, Walter Underwood wrote:
That “ideal curve” assumes an LC receive filter with a roll off on the high (and low) frequencies. That peak is a pre-emphasis on the high end to correct for the receive filters. Modern crystal filters and FIR filters don’t have that roll off, so it is not needed.
That's not true. There's nothing magic about "modern" filters -- filters implemented in DSP emulate filters made with physical components. ANY filter has skirts that we think of as only amplitude, but they also have phase response. Can't have one without the other. It's just that DSP filters can be made far more complex, so they can emulate physical filters that would be FAR too complex to actually build, so amplitude and phase response can be improved.
For ALL communications circuits where speech intelligibility is the primary goal, octave-band TXEQ should have the 60, 120, 240 Hz bands set for maximum cut, the 500 Hz band set by ear for something like 6-12 dB cut, the bands around 2.5-3.5 kHz should be set for 3-6 dB of peaking, and all other bands should be set "flat" -- that is, to 0 dB. In general, using "boost" EQ more than about 6 dB is a bad idea, because it tends to use up headroom and make it more likely that the signal path will clip on peaks.
In Elecraft rigs, the IF filters are in DSP. The only crystal filters are roofing filters, and they have that name because they protect the DSP filters from overload by strong signals near, but outside, the DSP filter's passband.
Maybe it works for your own voice and that’s great. But it is a choice, not a standard setting.
Yes. The settings I've listed are for a generic "flat" microphone, without a "tailored" response. Some ham mics, including some Heil and Shure models, have a peak around 3 kHz, and these mics should NOT be used with an additional 3 kHz peak in TXEQ.
BTW -- Bob Heil did NOT invent that concept. Shure was doing it in the earliest days of SSB (the '50s), and the D104 is a pretty old mic too. And the other great US mic company in those days was Electro-Voice, which was led by Al Kahn, K4FW, who later started Ten Tec when his partner, Lou Burroughs, wanted to sell the company and retire. Al was a CW man -- I don't know if they ever did any ham mics. :) But they OWNED the market for broadcast mics, and to some extent still do -- their RE20 is THE prestigious talk show and DJ mic, and their 635 and DO54 were wildly popular for reporters in the field.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
