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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!Xl.tags.giganews.com!local-4.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Tue, 19 Nov 2024 21:55:11 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: 80dB now but still needs improvement at 1KHz Date: Tue, 19 Nov 2024 16:55:11 -0500 Message-ID: <102qjjh5n2hr9b3mkmuibol68r4glc4fon@4ax.com> References: <1r37pyc.1bodve2fz5t4wN%liz@poppyrecords.invalid.invalid> <1r3a1m9.1lg1mngftnegwN%liz@poppyrecords.invalid.invalid> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 60 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-Md0BBrmubp757M6mNUFR2DJRlxjXpL/dguKp6S3cDgYOdHA2sEDv63UXZ1aDBcfFzE9JC0c2ki+WpAU!HwPVq/JcL2hCEIXqx6Fqnvz9sQlv+LWMsdEB/RmMW42ZuzJAqT5uPxeGT3MT8rCdtMLwJhU= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 3996 On Tue, 19 Nov 2024 12:16:05 -0800, john larkin wrote: >On Tue, 19 Nov 2024 13:50:46 -0500, Joe Gwinn >wrote: > >>On Tue, 19 Nov 2024 19:12:18 +0100, Jeroen Belleman >> wrote: >> >>>On 11/19/24 17:47, Edward Rawde wrote: >>>> "Liz Tuddenham" wrote in message news:1r3a1m9.1lg1mngftnegwN%liz@poppyrecords.invalid.invalid... >>>[...] >>>>> >>>>> The startup transient of the FFT would have to be included, so that may >>>>> set a limit to the accuracy of the simulation measurements. Even if you >>>>> start on a zero-axis crossing, you will get spurious results because of >>>>> the finite length of the sample. >>>> >>>> Yes I understand that. It's actually a sinewave multiplied by a rectangular function. >>>> That's why I try to use a sample length of many tens of seconds. >>>> A window function might help but then I'd have to decide which window to use. >>>> >>>>> >>>>> This can be demonstrated by doing FFT on samples of fewer and fewer >>>>> cycles from the middle of an apparently pure sinewave. As the sample >>>>> length decreases, spurious harmonics begin to appear, even though they >>>>> don't exist in reality. >>> >>>An FFT implicitly connects the end of the recording back to the >>>beginning. It's sufficient that the number of periods is integer. >> >>If testing with sine waves that all fit with an integral number of >>cycles per window, the FFT noise floor will be determined by the >>precision of the arithmetic used. >> >>But there is often a splice error at that join because the fit into >>the window is approximate, which is a good reason to use a window >>function. The default choice in the radar world is Taylor. >> >>Joe Gwinn > >I wouldn't trust LT Spice for simulating a low-distortion oscillator. > >Run a sim and zoom up on the top of some sine wave. It looks all >segmented and ratty. > >I was just simulating something and had a KHz range loop oscillation >that refused to be compensated. Turns out I had a BI behavioral >current source driving an inductor, and that oscillated all by itself. >A G current source does the same thing. > >At really low distortion, the opamp models can getcha too. Oh yeah. I don't use spice simulations unless I'm designing a circuit, which is rare these days. Mostly, I use Wolfram Mathematica, often with Bessel window functions (for phase linearity across the passband). Joe Gwinn