- Feb 7, 2009
REW is really nice
I will have to give REW a try again but my preferred method for audio analysis for the last few years has been to simply record a stimulus through the DUT into a hi res wav file and then analyze and plot with GNU Octave.trobbins said:Having some fun with REW ... with the aim of making almost distortionless sinewave test signal by adding in harmonics to null out harmonics generated in the line output of a soundcard (or even an amplifier under test).
My EMU0404 USB provides about a raw 0.0009% THD at 2Vrms from its line output. REW can be used to null the harmonics in that test signal to lower THD to around 0.00004% using a simple loopback test.
Shame. I took for granted that there is the option.I do not know of any way of doing this. It would be nice if the cursor followed the response like it does on LTspice.
Shame. I took for granted that there is the option.
I don't use projects, I just save the RTA graphs.Another thing I don't like is that you have to go through a few clicks in order to save an existing project.
warpie, not sure what you mean by 'project'?
Iif you are wanting to save a 'measurement' then the floppy disk symbol in the LHS listing of measurements will save the full details, as compared to using the camera symbol 'capture' which only saves what is displayed. And the File menu has a save all function.
In a Measure plot, I have not found a way to turn off the cursor lines/values - for example if I want a clean plot without cursors showing.
One hassle that may show up over time is that you may need the REW version used to make the data files to open the data files - or at least a later version.
I have found John to be extremely receptive to suggestions. Right after I mentioned unpractical limitations to the stepped sine measurements and lack of dBu measurements in the Level panel, he implemented it.One day I hope REW adds :
- calibrate-able dBu unit for RTA amplitude
- intermodulation distortion test measures
- a second 'measurement cursor' with the difference between them displayed ... like my Tektronix CRO
Best you use the REW forum to suggest any possible function tweak, such as regards cursor operation - but first search the forum.
It's a very good idea Ian, the phase diagram requires that there are two inputs to be compared by the software, one directly from the generator and one from the DUT, normally we need a splitter and a piece of software that can read the phase difference from two inputs (the reference and the signal coming from the DUT) ... REW would need to read the signal arriving on the sound card input (from the DUT) and the signal generated by the sound card (I think directly from the USB port) and sincerely I don't know if this is possible (I admit my ignorance). A small calibration routine will also be needed for phase zeroing. We could ask this question on the official REW forum.Oh, and automatic Q measurement of EQ plots - and Bode plots with phase response as well as amplitude.
I would define Q as the inverse fractional bandwidth at the half power points. This does not requires the filter to slope to infinity. It only has meaning if the filter response falls significantly either side of the half power points so it can only be sensibly measured at maximum boost or cut. Easy enough to find in an LTspice sim so should be possible in REW."ruffrecords said:
Oh, and automatic Q measurement of EQ plots "
For that it would be necessary first to define what is Q in an EQ.
The usual definition of Q is adequate only for filters that slope to minus infinite. An EQ slopes to unity.
In other words, Q is an inappropriate measure of an EQ's selectivity. I much prefer a definition based on perceived effect.
Of course, which is why I added the caveat that it only has meaning if the filter response falls significantly either side of the half power points. A filter with a max boost of 3dB clearly does not meet this criteria.Which results in Q=0 for an EQ that has a max boost of 3dB; I can only guess what Q is when the max boost is less than 3dB.