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Old 13th August 2009, 11:55 AM   #1
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Question measure amplitude of modulated signal

How must the amplitude of a modulated signal be measured, so that it can be compared to an unmodulated signal ?

With the cursor as in the picture ?

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Old 13th August 2009, 11:58 AM   #2
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Hi,

Depends what part you want to measure... the recovered signal, the average carrier or peak envelope power of the whole thing?

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Old 13th August 2009, 12:12 PM   #3
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I want to measure the frequency response of a sweep on CD to make corrections on the analog filter for a nonos DAC.
@ 20kHz it is already modulated like in the picture, and I am not sure how the amplitude should be to have a linear response.

The question might be, what does the ear detect, the maximum peak value or something else ?
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Old 13th August 2009, 12:18 PM   #4
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Ah, now we have this in context, you are witnessing "aliasing" - a beatnote when the sample frequency is (hideously complex math) with the recorded frequency.

When I encounter this, I usually try a different playback device

The ear detects average and when two signals are concerned, the linear sum.


Anybody that can be more helpful, jump in...

Cheers!
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Old 13th August 2009, 12:23 PM   #5
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Quote:
Originally posted by Geek


When I encounter this, I usually try a different playback device

The amplitude of the signal as shown in the picture shall be compared to a clean 1 kHz sine.

So the question is:

Is the response linear if the cursor keeps touching the curve during the sweep ?
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Old 13th August 2009, 12:25 PM   #6
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Quote:
Originally posted by Geek

The ear detects average and when two signals are concerned, the linear sum.
So RMS would be correct ?
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