Please help me understand mic behavior with REW

AustinJerry

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It seems to me that REW is very particular with respect to its connection to the mic, in my case a USB UMIK-1. When the mic is connected prior to launching REW, it performs as expected, showing ~50dB noise floor when opening the SPL meter. If, however, the mic is accidentally unplugged during an REW session, and then re-connected, the REW SPL meter shows a +30dB noise floor. There seems to be no way to recover from this situation other than to exit and re-start REW. And in another case, if REW is started without the mic being plugged in, REW refuses to recognize the mic if it is subsequently plugged in. Once again, the only recourse is to exit and re-start REW with the mic plugged in ahead of time.

Have I got this right, and is this expected behavior? I often hear of other REW users confused by situations in which the mic measuring level increases unexpectedly, or where users are having trouble getting the mic recognized at all. I would like to be able to provide the appropriate guidance.
 

skid00

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My AV System  
Main Amp
2 x Adcom GFA 555
Front Speakers
Carver Amazing Platinum Mark IV
I get no response in SPL meter if the mic isn't plugged in before I start REW...
 

John Mulcahy

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Apr 3, 2017
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There are differences in behaviour between Java and ASIO drivers.

Java drivers: If a device isn't connected when REW starts up it takes between 30 seconds and a minute (on Windows) for the Java runtime to report it as available after connecting it. It is then available to select. If a device that was being used is disconnected REW will revert to the default device, it will need to be reselected after reconnecting it, once it appears in the list.

ASIO drivers: The list of available inputs and outputs is obtained from the driver when the driver is loaded. If a device is connected afterwards it is necessary to reload the ASIO driver using the button on the soundcard preferences to get the new list of inputs and outputs. If a device which was being used is removed, causing an error, REW will revert to Java drivers. ASIO will need to be reselected.
 

AustinJerry

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Thanks for your response, John. I have performed the following test:

- Plugged the mic in and launched REW.
- Opened the SPL meter to verify noise floor ~50dB.
- Unplugged the mic, and then plugged it back in.
- Opened the SPL meter, noise floor now registering +30dB, or ~80dB.
- Opened Preferences, selected Java, then re-selected ASIO, and clicked Reload.
- SPL meter is still showing +30dB.

Am I not following exactly what you said to do? The only way I can clear the +30dB status is to exit and re-load REW.
 

John Mulcahy

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I think I see where the problem is. ASIO4All is a wrapper around the WDM drivers, so the Windows volume controls are still active. REW can read the input volume using the Java drivers and corrects the SPL reading accordingly. When the mic is unplugged the volume control disappears and starts returning zero as the input volume setting, so REW starts correcting for the 31 dB of attenuation that is applied at the zero volume setting and the SPL reading shifts up by the difference between the original volume setting and -31 dB. I'll think about whether there is a way to deal with that.
 

John Mulcahy

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I have added a workaround in the next beta to deal with a USB mic being disconnected and reconnected while REW is running. Note that if the mic is disconnected while REW is capturing audio that will cause an error.
 

AustinJerry

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Thanks for getting to the bottom of this. Perhaps something as simple as a pop-up message saying "REW has lost the connection to the microphone. Please re-connect the microphone and re-start REW to restore functionality".

I have on occasion accidentally disconnected the mic as I was moving the mic stand around for measurements at different positions, probably caused by a loose USB connection. I am sure others have experienced this as well, and became confused when the mic "lost its accuracy".
 

John Mulcahy

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Perhaps something as simple as a pop-up message saying "REW has lost the connection to the microphone. Please re-connect the microphone and re-start REW to restore functionality".
REW doesn't know the mic connection was lost. The volume control continues to behave as if the mic was there but just returns zero as the volume setting, which is an allowable value. The workaround doesn't require REW to be restarted.
 
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