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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Hi John posted by jneutron on June 13, 2003 at 12:47:00:
Jneutron, who says that HP has ever made any equipment that has that specific resolution? I am using a TWO STEP process. The Sound Technology seems happy enough, so long as I can process out the noise. The HP FFT analyser only processes the distortion residual, so it doesn't have to be as precise as you might think, because it's tough to add significant distortion to distortion itself. Think it through. The original signal is nulled 95dB and the distortion products are boosted 50db so that the residual that we have to work with is -45dbV down to maybe -65dbV. The FFT analyzer, whether it is the 'Mac the Scope' FFT program on my MAC, or the HP3563, it has a pretty reasonable level to process the harmonics. You can do it too, with your sound card, IF you can make an active or passive null for your test signal, then amplify it very cleanly, perhaps 40-60 dB to get the level of the distortion products up to a level where you can cleanly process them. I recommend using, like Victor, and others, the AD797 op amp to post amplify the distortion products, after the null.
Unfortunately, the presence of the 1K to 5KHz test signal will make almost any direct FFT measurement useless, because the harmonics will be in the mud of the FFT analyzer. Once again, this is why we have to NULL the test signal first.
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Follow Ups
- Re: Hi John - john curl 15:24:22 06/13/03 (2)
- Hi John - jneutron 19:05:25 06/13/03 (0)
- Re: Hi John - Steve Eddy 16:13:10 06/13/03 (0)
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