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In Reply to: Link posted by Ugly on August 16, 2015 at 16:48:57:
It took me a few posts to understand that you were confusing the test signal @ 60Hz with a hum problem. I thought you were commenting on the power supply spuria at -110 dB, which are a problem IMO for someone trying to measure the performance of digital sources.
The SMPTE IMD test is a legacy test that's been around for many decades. Like I wrote to Tony, I didn't realize anyone was still using it. My ignorance. I don't think it's a good choice of frequencies. I also don't think it's being implemented properly by the RightMark software, otherwise the reported level would be much lower.
But I don't understand what your complaint is with the 60 Hz component of the test signal. I'm confident that the test signal is a pure 60 Hz tone mixed with a pure 7 KHz tone, and the way the peak looks in the FFT is determined by window type. It looks like a flat-top window to me. If your complaint is the width of the peak, that's mainly due to the log frequency scale, and secondly a function of the window type.
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Follow Ups
- Glad you finally got that - Dave_K 06:49:10 08/17/15 (1)
- RE: Glad you finally got that - Ugly 07:46:51 08/17/15 (0)
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