Hi Christian...Time for me to ask a question or 2 and seek your assistance
When I use REW, I do it in a basic form just to get fr sweeps.
I use a windows laptop with a calibrated Dayton IMM6 mic. Input and output from the TRRS headphone/mic jack wired to a Bluetooth amp thence to the speakers. Not lab standards I know but ok for my needs.
This gives me the FR graphs but no timing signal and the generate button in the spectrogram window is greyed out..
I'm unclear as to how to incorporate a timing signal and get the generate button active. Seems to be a common question on the web but I haven't found a clear answer and despite 300+ pages of the help file I'm still not sure of the process.
I presume the timing signal can be sent to the speaker being tested so no more hardware need be involved?
Cheers
Eucy
Hello Eucy,
I try an answer in 2 steps...
1/ Your setup seems to me enough to get some timing information as REW can send its signal to an amp (no matter where the DAC is), the amp drives the loudspeaker, the mic collects the sound and is connected back to the REW. There are papers telling that such set up (which roughly also mine) is not precise enough to get real timing information due to some jitters in the interfaces (case of USB mics, see Virtuix tool web site) but i think it is not the problem here.
2/ REW offers at least 2 ways to get an FR:
2.a/ One is thanks to a pink noise available in the generator tool with a reading with the RTA (see screen shot below). This is a good technique to make some averaging over your listening area (see on the web "Moving Microphone Measurement") but you can't get timing information from it
2.b/ The second is thanks to a log sweep you access by the measure icon on the top left corner. When the log sweep is recorded, the IR is generated, the time information is available. See slide 3 of my document to launch the measure, slide 6 to see the Impulse response.
If you are in case 2.a, easy, make tests according to 2.b
If you are already in 2.b... more tricky... The chain of information could make the time information wrong (see before the jitter in the interfaces) but for now i don't see why it is missing.
Perhaps 2 additional comments :
- There is no need of calibration of the measurement chain. it is of course better for the precision but not mandatory.
- Some interface like the mic input of a laptop can seriously modified the measurement due to their strong performance limitations but this not a reason not to have the time information... it is just a bad measurement ;-)
so 2.a or 2.b ?
Christian
Hi and thanks Christian
I'm 2b..I use the log measurement sweep method but get no timing information.. Saved measurements say timing info is missing..I tried uninstalling and reinstalling the program but no difference
Am I missing a setup step maybe?
I'll try again when I get home...a few more days to go
More plywood and 6 more exciters waiting for me there. 😄👍
Regards
Eucy
I'm 2b..I use the log measurement sweep method but get no timing information.. Saved measurements say timing info is missing..I tried uninstalling and reinstalling the program but no difference
Am I missing a setup step maybe?
I'll try again when I get home...a few more days to go
More plywood and 6 more exciters waiting for me there. 😄👍
Regards
Eucy
Hi Leob
I can't recall the settings. I'll have to check when I get home
It's bound to be something simple and stupidly overlooked
Thanks
Eucy
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Sometime the simplest solution is the right one, sometime not... but always start with it!
REW proposes to store the measurements in a .mdat file. If you want to zip and post one, i can have a look.
A schematics of the measurement chain could also help.
Do you have the possibility to test without the bluetooth? Only with wires or at least usb?
I am going to make some tests, I will look more carefully to the setting.
Christian
PS
@Leob : sorry I haven't seen your post before replying... good proposal. I will check more carefully my (basic) setting too... but I guess you have solved the issue.
@Eucyblues99 , @Leob
Making some measurements this afternoon, I had a more careful look at the settings.
I think what you suggested Leob is the root cause of the problem but not the only explanation.
My understanding is REW offers 3 possibilities to get a reference for the time.
1/ "No timing reference" / "set t=0 at IR peak" : it is what I use. The time origin is at the peak of the impulse. This option is not suitable to work with several drivers but in the case of the DML as there is only one source, it seems not a problem
2/ "use loopback as timing reference" : here a second channel is used (loop back) to reference the measurement. The best choice
3/ "use acoustic reference timing" : it seems (I haven't closely checked) like a trigger in an oscilloscope. So in case a loop back is not possible in a multi source measurement, it is a better than 1/, not as 2/
So I tested the 3 on my laptop.. the 3 works!
My assumption is your are in option 2/ but something in the setting makes muted the channel where REW is expecting the second signal.
Below are the preferences/souncard of my REW.
I use the left channel of the input (usb microphone) and the right for the loop back.
The mic is mono but is seen as a stereo device.
Under Audacity, the 2 channels of the monitoring meter move the same.
The second hypothesis to explain your problem is your mic has no left and right channels
Suggestions :
- set to 1/ "No timing reference"
- set to 2/ "use loopback..." AND in the preference/soundcard set the loopback input on the same channel. I am going to think about this setting for my own use...
Let us know if the problem is solved... or not...
Christian
PS : I connected an analog phone head set (TRSS jack = 4 poles). Under Audacity, the mic appears only on the left channel. It gives sens to the assumption.
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Thanks Christian
Bluetooth is not used in the measurement chain..
The IMM6 mic plugs directly to the laptop headphone jack, and the output cable plugs to the IMM6 output jack thence to the amp input via a 6m cable
Re mic channels ..I'd assume the mic is mono since it's meant as a test rather than a recording device ???
Thanks for help guys
I'm hopeful for the outcome
Eucy
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PPS.
I should also mention that the reason my mic is attached directly to the laptop is that the TRRS extension cable I purchased causes considerable interference... buzzing... Also a problem which is reported commonly on the web.. Seems to be a grounding issue. One guy reported trying multiple cables and all have the same problem so trying different ones may be a long and expensive process... (Unless someone here can recommend a known working cable)
Eucy
I should also mention that the reason my mic is attached directly to the laptop is that the TRRS extension cable I purchased causes considerable interference... buzzing... Also a problem which is reported commonly on the web.. Seems to be a grounding issue. One guy reported trying multiple cables and all have the same problem so trying different ones may be a long and expensive process... (Unless someone here can recommend a known working cable)
Eucy
Eucy.
When I tried using microphones with my laptop, I had the impression that the noise was caused by bad internal screening in a very noisy environment inside the computer.
So changing the external cable would make no difference?
The only way to get around the problem, would be to have an external dac (sound card).
Steve.
When I tried using microphones with my laptop, I had the impression that the noise was caused by bad internal screening in a very noisy environment inside the computer.
So changing the external cable would make no difference?
The only way to get around the problem, would be to have an external dac (sound card).
Steve.
This could be why I coated the panel in yellow vinyl silk, to dampen the self noise .
I will make a recording of this panel ,to show how it performs .
Even in its beaten up state.
Steve.
Hi Steve
In my case it's the cable... Plug the mic directly into the laptop and all is well
The extension cable issue is well reported on the net
Eucy
Yes it depends on how it is internally manage into the laptop. Audacity gave good information.
The quality of the jack extension cables is a problem. I think for cost reasons few are shielded.
An other possibility is you add an adapter at the laptop port to have one stereo jack for the signals output and one mono for the mic. and then a cable with a shielded cable suitable for a mic.
This needs probably to order some parts and to make some welding. The splitters seem quite common on the net. The cable is specific (jack mono to the Dayton mic TRSS).
By the way, I am not really confident in the noise or bandwidth performance of the laptop mic input. they are designed for the voice not for audio... so an external DAC is a good solution.
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So.....In for a penny, in for a pound..
I just ordered a Behringer Umc22
I'm going to makes up a cable to fit my Dayton IMM6 mic. I considered the Behringer 8000 but it seems to be a questionable item and probably no better than the IMM6
Question... Will the IMM6 need the 48v phantom power ? or will using it blow up the mic🤔
Cheers
Eucy
I just ordered a Behringer Umc22
I'm going to makes up a cable to fit my Dayton IMM6 mic. I considered the Behringer 8000 but it seems to be a questionable item and probably no better than the IMM6
Question... Will the IMM6 need the 48v phantom power ? or will using it blow up the mic🤔
Cheers
Eucy
Hello Eucy
The IMM6 is in my understanding (not written like that in the documentation but "condenser") an electret microphone. If it tells to you, you can see the 2 terminals of the mic as the source and the drain of a jfet. The basic interface is to load it with a resistor connected to a supply. When the device is portable, the voltage is something like 2.2V or 5V, the resistor some k.
So no direct voltage on it and certainly not 48V. Higher voltage than 5V might be possible with the right resistance in series so that the maximum voltage across the mic is not reached.
I suggest you search around electret and their interfaces and what are the options of the UMC22.
I will see later if I can be pore precise.
Christian
With some schematics from my notes :
The IMM6 is in my understanding (not written like that in the documentation but "condenser") an electret microphone. If it tells to you, you can see the 2 terminals of the mic as the source and the drain of a jfet. The basic interface is to load it with a resistor connected to a supply. When the device is portable, the voltage is something like 2.2V or 5V, the resistor some k.
So no direct voltage on it and certainly not 48V. Higher voltage than 5V might be possible with the right resistance in series so that the maximum voltage across the mic is not reached.
I suggest you search around electret and their interfaces and what are the options of the UMC22.
I will see later if I can be pore precise.
Christian
With some schematics from my notes :
Attachments
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