Amplitude variations between spectrum+Channel Meter Bridge

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subboy
Posts: 7
Joined: Thu Nov 13, 2008 8:44 pm

Amplitude variations between spectrum+Channel Meter Bridge

Post by subboy » Wed Apr 24, 2013 11:40 am

Im getting different Amplitude readings between the spectrum Analyser and the Meter Bridge on the track channel. Is this because the Meter Bridge on the channel strip is outputting Peak Levels and Spectrum is outputting RMS levels ? If so is there anyway to change the level mode inside Spectum to output True Peak levels as DBFS . I want to use spectrum as a tool to measure not only the frequency of a sound but also the DBFS peak levels.

73*
Posts: 34
Joined: Sat Dec 01, 2012 11:03 pm

Re: Amplitude variations between spectrum+Channel Meter Bridge

Post by 73* » Thu Apr 25, 2013 4:27 am

When you say that you want the spectrum analyzer to output 'True Peak levels as dBFS', I am assuming that you're wanting to the spectrum analyzer to display the peak amplitude of the entire signal. If that is in fact what you desire, the answer is no.

The solution to your problem is that you are simply going to have to rely on two types of meters to get the two types of information that you desire... I would recommend voxengo's span (http://www.voxengo.com/product/span/), it's free and it has both peak and spectrum metering in the same plug in. At least that way you're only dealing with one window.

/* Very brief technical explanation of why (avoid if you don't like those sorts of things) */
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Examining a signal in the frequency domain is different from analyzing it in the time domain. There are methods to switch between the two domains (Fourier & LaPlace transforms), but that doesn't mean that you can show both types of info on the same graph.

A spectrum analyzer calculates and displays the (approximate) magnitudes of a signals spectral components, the resolution/accuracy of this representation is limited by the mathematical methods and the size of time windows used in performing the calculations.

The actual peak amplitude of a signal (True Peak as you said) is simply the magnitude of the signal at that specific instant, in the digital domain it would simply be the value of the sample for that instant in time. This single number does not tell us anything about the spectral components of the signal that generated it (if you're at all familiar with math or physics, what's the frequency of a signal with a period of 0?). Calculating the RMS levels of complex signals involves using time windows (for averaging), but this is normally done in the time domain and as a way to present us with an estimate of the power of a signal.

With that said, this is a very deep and well developed area of mathematics, so a lot of time could be spent learning and discussing it. If you are interested in getting a bit of knowledge in this area here are a couple sites worth visiting.

http://www.engineeringvideos.org
http://www.falstad.com/fourier/
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Jack McOck
Posts: 869
Joined: Tue Apr 16, 2013 12:06 pm

Re: Amplitude variations between spectrum+Channel Meter Bridge

Post by Jack McOck » Thu Apr 25, 2013 7:50 pm

You're welcome.

:x

subboy
Posts: 7
Joined: Thu Nov 13, 2008 8:44 pm

Re: Amplitude variations between spectrum+Channel Meter Bridge

Post by subboy » Fri Apr 26, 2013 12:58 pm

73*: Thanks for the advice and extra info, I will take a look at the Voxengo span.
:D

Jack McOck
Posts: 869
Joined: Tue Apr 16, 2013 12:06 pm

Re: Amplitude variations between spectrum+Channel Meter Bridge

Post by Jack McOck » Fri Apr 26, 2013 5:27 pm

Order is restored.

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