HF Shelf on Stimuli

[tomrbland]

Is it possible to add a HF shelf to the Stimuli? The noise floor of a larger space is often very LF heavy leading to increased sweep levels. However we don't need all that hf energy and it just blows your head off if you're not careful. A user selectable 6/12/18dB hf shelf would really help.

p.s. so would being able to put measurements into folders if anyone knows how to achieve that!

 

[John Mulcahy]

I'll add shaped stimulus to the todo list, but it won't reach the top of the list any time soon.

You can save measurements anywhere you like, so not really following the folders comment.

 

[tomrbland]

Thanks John, that's great news. I think once that comes in I'll be able to switch across to REW for my day to day measurement software! I can't use it on all of my systems at the moment because the HF just gets a bit extreme without the shaped stimulus and people working in the space get a bit grumpy!


The folders comment really comes into play if you have lots of loudspeakers all in the same space. You can see an example in the Smaart UI. I was tuning a large distributed system the other week and as I was taking a couple of measurements across the coverage area per loudspeaker but due to the number of measurements through the space the work flow became: New file per loudspeaker, create the average for that loudspeaker, and then create a new file and bring in all of the averages from all of the loudspeakers in the space to create the average of the space. Would just be neater if I could have done it all in one place. But it's no biggie.

 

[John Mulcahy]

If you right click in the All SPL graph legend area there are some options that may help with choosing which measurements to include in an average, but more general methods for grouping measurements based on some characteristic are one of the many things on the todo list.

 

[pklose]

If you are on a Mac: I have hooked Soundflower Rogue Amoeba in between the REW O/P and the measurement DAC. Works reliable.

 

[John Mulcahy]

If the sweep is altered after it leaves REW the shape of the alteration would need to be loaded as a cal file to get the correct frequency response, or merged with the IR to get a correct impulse response.

 

[pklose]

of course, I just wanted to show a way to alter the sweep on the way out.

 

[tomrbland]

I had another brain wave on this. On my current project I am using the playback from file option quite extensively (hosting the file on a Q-SYS player). So I took the generated file and ran it through an EQ and then tried to load it into REW. But I get the error "The file does not contain the data REW requires". I presume this is a check against the WAV Header as that's the only thing I can think that would change after rendering out of Reaper in the same format. Would it be possible to just defeat this check to allow for stimuli with different responses to be used? The workflow would be:

- Generate file with generator
- Post process file in reaper or similar
- Render to same format
- Load to playback device
- Load to REW to use as the reference

 

[John Mulcahy]

That isn't possible, sorry. REW only looks at the first couple of dozen samples of the sweep file as sweep parameters are embedded in the least significant bits, it then uses that info to generate the corresponding sweep function, avoiding any limitations of the file format.

 

[tomrbland]

Doh! Thought I might be on to something for a minute. Thanks for clearing that up for me though.

 

[John Mulcahy]

There is a way to experiment with a shaped stimulus if REW is the playback source by using the "Use loopback as cal and timing reference" mode and selecting "Merge loopback response into IR". If you set up some filters (e.g. some shelving) in the EQ window and then select "Measure with these filters" in the Filter tasks pane REW generates a sweep with the chosen filters applied to it. When the timing mode is "Use loopback as cal and timing reference" the same filtered sweep is output on the reference channel and the response of the reference input is used to correct the measurement channel. It would probably be convenient to save the filters you want to use and load them in the EQ filters window before you measure, since the filters will be reset for each new measurement. Alternatively set the filters up in the first measurement and keep going back to that and using "Measure with these filters".

 

[tomrbland]

I'll add shaped stimulus to the todo list, but it won't reach the top of the list any time soon.

You can save measurements anywhere you like, so not really following the folders comment.

Hey John, any news on the shaped stimui? I don't think I've spotted it in the releases (unless I can't find it).

 

[John Mulcahy]

Nope, still a long way off, sorry.