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Discussion Starter #1
I have encountered a bug with REW and the FBQ2496, affecting all EQ settings that are sent as BOTH channels to the FBQ. It's most noticeable with a full-range signal. After sending EQ settings via 'both' channels (not separately) to the FBQ via REW, a power cycle of the FBQ will introduce an audible shift in the signal, noticeable in the higher ranges. To my ears, it sounds like some sort of phasing issue.

This can be fixed by holding the left/right button to revert to one channel, and then repeating to copy the channel back over (only works when using the same EQ for both channels). The result is that it sounds like when the filters were originally copied over from REW (before a power cycle of the FBQ). I have confirmed this with two separate FBQs and multiple EQ settings.

Even though my use is for a full-range signal, this affects sub-only use, as well. I wonder if the reason I can't find any information on this is because the shift is not as noticeable given the frequency range and the ears' sensitivity to anomalies in the higher frequency ranges.

A workaround that I have found is to send the signal via the LEFT and then RIGHT separately, instead of the BOTH option. A power cycle does not shift the sound. It seems that there is something up with the BOTH option, possibly across multiple EQ boxes. AFAIK, this issue has existed since the addition of the BOTH setting. I remember using the separate LEFT and RIGHT and never having this issue.
 

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The Midi messages REW sends are the same whichever bank is chosen. A Left, Right or Both bank selection message is sent before the filter messages (note these bank options have no connection at all to REW's audio output channel selections). All 3 bank options have been offered for as long as the FBQ has been supported. If something odd happens after a power cycle I'd be inclined to label that an FBQ bug, not an REW bug.
 

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Discussion Starter #3
If something odd happens after a power cycle I'd be inclined to label that an FBQ bug, not an REW bug.
It definitely does strike me as an FBQ bug - it's good to know that the filters are not processed differently by REW. The point is that anyone using the FBQ and sending BOTH filters at once will have problems with their signal once the FBQ is power cycled. I was able to test on two FBQs with the same result. If this can be confirmed, it may make sense to remove the 'both' option.

All 3 bank options have been offered for as long as the FBQ has been supported.
I have also used a dsp1124 previously - that may be the one where the 'both' option was added at a later date.
 
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