# True RTA and signal generator



## Guiria (Jun 15, 2008)

I recently purchased True RTA to calibrate my sub with EQ since I was never able to get REW to work with my current hardware properly.

I used the Avia disc and it's LFE sweep as my signal to EQ my sub. 

My question is what other signal generators could I use that are not so long as the sweep in the Avia disc? That one just takes too long, plus navigating the tracks to repeat the sweep is a little cumbersome. 

I'd prefer a sweep using my laptop and not the DVD player. I've used the signal generator in REW but it seems that the response has constant peaks and dips unrelated to room modes; far more in fact compared to using the LFE sweep from the Avia disc. Both tests were done using the 1/24th/octave resolution. Perhaps I should just decrease the resolution?

I thought TrueRTA had a sweep feature in it besides the quicksweep. I use an RS digital SPL meter and the quicksweep is too fast to plot anything consistently.

What are your thoughts on sources that will allow me to generate a 5-10 second sweep that will produce acceptable plots for me to work with?

Thanks.


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## brucek (Apr 11, 2006)

> 've used the signal generator in REW but it seems that the response has constant peaks and dips unrelated to room modes;


I don't really understand this? The signal generator in REW produces a sweep that you can select different lengths and any bandwidth you want. Peaks and Dips?

Also, at the bottom of the download page, we have a sinewave file that has four subwoofer sweeps that you can download and burn to a CD.

brucek


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## Guiria (Jun 15, 2008)

brucek said:


> I don't really understand this? The signal generator in REW produces a sweep that you can select different lengths and any bandwidth you want. Peaks and Dips?
> 
> Also, at the bottom of the download page, we have a sinewave file that has four subwoofer sweeps that you can download and burn to a CD.
> 
> brucek


Let me try again, when I use the signal generator in REW say from 10 Hz to 200 Hz I get a series of peaks and dips in my response that I do not get when I use the Avia disc's LFE sweep. Perhaps REW and Avia use different sweep methods but I think both are sine wave sweeps. Now that you have me thinking about it, could the difference be in the RS meter's ability to pick up the signal being played. The Avia LFE Sweep is really long, probably 40 seconds or something like that from 100 Hz down to 20 Hz. The REW sweep is 5 seconds.

I'll check out the test tones on the link...Thanks.


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## Dent (May 6, 2006)

Maybe with the REW sweep, you have the tones coming out from both the mains and sub whereas with the Avia LFE sweep (due to it being LFE only) it is coming out from only the sub. If the mains and sub are both playing with the REW sweep then you will have interaction affecting the response which you won't have with a sub only output response.


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## Guiria (Jun 15, 2008)

Dent said:


> Maybe with the REW sweep, you have the tones coming out from both the mains and sub whereas with the Avia LFE sweep (due to it being LFE only) it is coming out from only the sub. If the mains and sub are both playing with the REW sweep then you will have interaction affecting the response which you won't have with a sub only output response.


You are right, with REW the mains are involved, which is a good explanation of the response differences. I will have to try some things out tonight to see if that is the root cause of the difference in response. So far, that is the most logical explanation of what is happening.

I also downloaded the sweep files so that will definitely come in handy.


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## Dent (May 6, 2006)

Using REW, when I want to see my sub only response, I disconnect the mains speaker wire going into the AV receiver. With this way, the internal crossover/bass management of the AVR is still functioning however. I believe with the LFE sweep, there is no crossover/bass management involved so the responses of the sub only may still be different with the REW way and the AVIA sweep way. To get the situation identical, you could plug the output from REW directly into the sub instead of into your AVR.


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## JohnM (Apr 11, 2006)

James,

You may be misunderstanding the test signals to use. TrueRTA (and RTAs in general) can be used to view frequency response if you use a broadband pink noise source as the test signal. The pink noise excites all the frequencies and the RTA shows the level within its frequency bands. To use an RTA in that way you should use a pink noise test signal. Sweep signals are not for use with an RTA. The sweeps in REW and the quick sweep in TrueRTA are for use when the software is operating in a mode in which it captures the response to the sweep and then calculates the frequency response, they are not for use with an RTA display.


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## Guiria (Jun 15, 2008)

JohnM said:


> James,
> 
> You may be misunderstanding the test signals to use. TrueRTA (and RTAs in general) can be used to view frequency response if you use a broadband pink noise source as the test signal. The pink noise excites all the frequencies and the RTA shows the level within its frequency bands. To use an RTA in that way you should use a pink noise test signal. Sweep signals are not for use with an RTA. The sweeps in REW and the quick sweep in TrueRTA are for use when the software is operating in a mode in which it captures the response to the sweep and then calculates the frequency response, they are not for use with an RTA display.


I see, so if I'm using TrueRTA for in room frequency response measurements should I be using a pink noise test signal or a third party signal generator? I'm primarily capturing 200-10 Hz for subwoofer EQ'ing. What frequency range do pink noise signals cover?


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## JohnM (Apr 11, 2006)

You can use pink noise from a test disc or from a generator like the one in REW. Strictly speaking pink noise should cover the full frequency spectrum, but it can be filtered to cover only a selected band - for example, the level setting signals in processors are usually filtered pink noise, thoguh they cover too narrow a band to be used to look at frequency response. To select a filtered pink noise signal in the REW generator select the "custom" option of the pink noise signal and set the "High cut" to 400Hz and disable the "Low cut" (uncheck the box).


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## Guiria (Jun 15, 2008)

Not to resurrect a dead thread here but in all fairness to REW...I finally got it working and using it is way easier for measuring in room frequency response than using TrueRTA.

The problem I had was the low level, check input volume message. In the settings>soundcard tab the input channel was always set to right. Once I checked the left channel everything worked flawlessly

I've worked in IT before and I can honestly say that 90% of these types of problems are user error, why it took me so long to figure that out, I don't know


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