## News:

### Author Topic: rms values from power spectral density graph?  (Read 13519 times)

0 Members and 1 Guest are viewing this topic.

#### Neill

• Newbie
• Posts: 1
##### rms values from power spectral density graph?
« on: June 15, 2009, 10:42:41 AM »
I am looking at the SignalPro program on the iPhone as a tool for doing portable vibration analysis on products that are undergoing vibration testing.  A key parameter that i need is grms.  Is this number calculated and displayed in SignalPro?  If so, is the bandwidth of the calculation user settable?

If I understand correctly, it is possible to bring two channels of line level signal into the iPhone at the same time (left and right line input).  Is this correct?  If so, can I do analysis on both channels simultaneously?   (edit - nevermind - I see that I can).

Thanks for the help here.  I don't know if this is the right place to ask these general questions, but I figured others might benefit from the answers.

Neill
« Last Edit: June 15, 2009, 11:27:03 AM by Neill »

#### FaberAST

• Sr. Member
• Posts: 320
##### Re: rms values from power spectral density graph?
« Reply #1 on: June 15, 2009, 11:27:55 AM »
Neill,

Quote
Is this number calculated and displayed in SignalPro? If so, is the bandwidth of the calculation user settable?
Currently, the Octave tool will measure and display grms in either whole or 1/3 octave bands. Alternatively, you can measure signal amplitude as a function of frequency in the FFT analyzer. In that case, you'll need to divide the magnitude by the square root of 2 to get rms at a particular frequency.

Quote
If I understand correctly, it is possible to bring two channels of line level signal into the iPhone at the same time (left and right line input).  Is this correct?  If so, can I do analysis on both channels simultaneously?
This is correct for the FFT and Oscope tools. However, the Octave analyzer can only handle a single channel. To get two-channel data into the iPhone or iPod touch will require an audio input device that attaches via the dock connector. Some options are discussed in a recent blog post.

Quote
I figured others might benefit from the answers.
Exactly right. Thank you.

Ben