On Tue, 02 Sep 2008 17:06:29 +0100, Brendan Minish wrote: >I used an old copy of SMAART pro that I have from my Sound engineering >days.
I have that software, and have long used it to analyze ham filters. >the sound card is a delta44 I don't know this card, but it's own noise floor (or input stage) may be the limiting factor. Look at the first data set in http://audiosystemsgroup.com/K3FilterStudy.pdf The black curve (the Headphone output) and the red curve (Lin Out) are set to produce the SAME output level, but the harmonic distortion is 55 dB stronger at the Line Output! The difference between the LF traces is IM, and is also significantly greater at the Headphone output. Notice also the dynamic range of this measurement, which is 90 dB. The excitation is band noise, so there's another 10 dB or so between the top of the screen and digital clip. My measurement system is EASERA SysTune (considerably more advanced than Smaart Pro), and the input device is the EASRA Gateway, which has a 24-bit A/D and Firewire interface. I'm fairly confident that the noise floor in my measurements is the radio, not the measurement system! That first data screen shows 3rd harmonic at -55 dB for a gain setting of 1 (and that is the noise floor of the radio). At a gain setting of 2, it's -54 dB. At a gain setting of 3, it's -49 dB. At a gain setting of 5, it's -40 dB. For a setting of 10, it's -28 dB, and at 20, it's - 29 dB. Note also the very significant difference in excitation. My test signal is not a CW signal, but broadband noise from an antenna, band- limited by the IF filters. Your test signal is a sine wave. My test signal is somewhat representative of trying to copy a signal in QRN, or pick one signal out of many in a contest. Your signal is representative of a test bench or a signal with little or no noise on it. As I'm sure you know, those of us working in pro audio find pink noise far more useful than sine waves help us hear real world problems in systems. 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
