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Old 10th November 2017, 09:19 PM   #391
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by luckythedog View Post
Just to clarify in principle.............

With sphericals, the incremental effect of misalignment is mostly geometric harmonic distortion only........which is small and audible in the scheme of things for real programme material.

LD
Ooops I mean 'small and inaudible'.............

LD
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Old 11th November 2017, 07:03 AM   #392
fasterbyelan is offline fasterbyelan  United Kingdom
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Originally Posted by scott wurcer View Post

BTW - I wish everyone would stick to pitch, roll, yaw, x, y, z.


I always have trouble with this, may be it's due to my time spent working on radar........... and aircraft/racing cars!
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Old 11th November 2017, 01:19 PM   #393
oneoclock is offline oneoclock  Europe
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Need to measure intermodulation distortion 4400 Hz.

The program need tow filters 4400 Hz for IMD and 4000 Hz for normalize.

The variation is of 1% order respect to 4000 Hz amplitude in dB. Is important to maintain the 4000 Hz amplitude reference al time for correct measure because the amplitude of 4000 Hz and 4400 Hz will oscillate all time also of the 1% order in dB.

It can also be easily measured with a spectrum analyzer: Audition, Sia Smaart Live.....

Click the image to open in full size.
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Old 11th November 2017, 01:42 PM   #394
scott wurcer is online now scott wurcer  United States
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Originally Posted by oneoclock View Post
Need to measure intermodulation distortion 4400 Hz.
No the 4400Hz and 3600Hz are the AM/FM sidebands (first two). You can not look at just one. The demodulation of the 4k is what you want separated into AM and FM components.
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Old 11th November 2017, 02:17 PM   #395
oneoclock is offline oneoclock  Europe
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Now I understand. The correct measure would be to include all the intermodulation products.

I have observed that the first two 4400Hz and 3600Hz are the most representative. I have seen with Audition that the following intermodulation products are less representative: 3200 and 4800, 2800 and 5200, 2400 and 5600, ..... more similar among them as they move away from 4000 Hz.

In a spectrum analyzer, observing one of these two sidebands can be a sufficient approximation (like 1 dB). But with all the products, the measurement will be more precise (like 2 dB or more).

Last edited by oneoclock; 11th November 2017 at 02:21 PM.
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Old 11th November 2017, 02:33 PM   #396
scott wurcer is online now scott wurcer  United States
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Yes, one problem is that the sidebands are spread out by noise so a simple look at the spectrum does not give a magnitude or phase reading. You have to demodulate and filter.

If you synthesize a mathematically perfect signal then you can just read the spectrum.
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Old 11th November 2017, 03:44 PM   #397
Hans Polak is offline Hans Polak  Netherlands
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A few more images from Scott's Normal.Wav recording.
The left image is showing for the Left and Right channel the incoming 400Hz from the LP plus the demodulated 400Hz IM product from the 4KHz before being chopped into positive halves as in the RCA patent.
The 400Hz in blue is out of phase between L and R, confirming vertical modulation of the mono signal, but the IM products in red are in perfectly in phase.

The image to the right is showing again the same demodulated IM signal from the 4KHz, but now for a whole revolution of the LP.
The glitches that are visable, are only there for part of the track and mostly 40msec apart at closer inspection.
Next to the time signal, a 25Hz peak is clearly visible in its spectrum.

Scott, this was the 25Hz that you also noticed, but because these glitches are only there for some part of the track, it doesn't seem to me to be a rumble product coming from your TT.
Could it be that the cutting machine produced this artefact ?


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Old 11th November 2017, 04:12 PM   #398
Hans Polak is offline Hans Polak  Netherlands
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Here another image showing the demodulated 400Hz signal from the 4Khz, but now for both channels and again for one full LP revolution.
The glitches in this demodulated signal are not at identical moments for L and R, indicating again in the direction of the cutting machine ?


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Old 11th November 2017, 04:19 PM   #399
scott wurcer is online now scott wurcer  United States
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I have no idea where the 25Hz comes from. I have to apologize for my misunderstanding of the crosstalk test. The left - right - stereo sequence is for shall we say roll and yaw. The RCA test is supposed to be for pitch, I think. I also think the roll and yaw need to be very good before doing the other test or there is too much contaminating information.
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Old 11th November 2017, 04:32 PM   #400
Hans Polak is offline Hans Polak  Netherlands
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And here some random examples of glitches with magnified time-scale, left channel green and right channel in red.
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