Originally Posted by Audionut11
The mini-dsp will work best with it's input/output levels at maximum. Since the Rev b. has 7.5 dB of insertion loss
, you should probably have it configured in Rev a. This means 0.9v input/output.
So you want the AVR outputting 0.9v maximum, so as not to clip the input of the mini-dsp. Generate some pink noise with REW at -3 dB, and the AVR main volume control at -0 dB (or whatever is your reference level). Set the sub trim on the AVR at a point where the input level meters on the mini-dsp begin to drop/raise. In other words, if the mini-dsp input meters are at 0.0dB @ -8 dB AVR sub trim, then any higher is simply clipping. Set the AVR sub trim to the point just before clipping.
Adjust sub levels as needed.
If you run Audyssey afterwards, you should double check the AVR sub trim setting. If it has been raised (ie: -3 dB instead of -8 dB as the example above), you should increase the gains on the subs.
If the AVR sub trim has lowered (say -12 dB), you should reduce the gains on the subs.
How close you maintain the input level of the min-dsp to 0 dB after all is said and done, is you're own decision on benefit/time.
Until your post, I was unaware that there were two revs of the MiniDSP 4x2. I checked mine, and it is indeed a Rev A. Not sure how I got a rev A because it was purchased less than 6 months ago, and I don't recall at purchase time being asked which rev I wanted. I assume as long as the proper procedure is followed, this will not be an issue.
Sorry for so many questions, but I would like to understand and follow your procedure.
- When you say generate pink noise at -3dB using REW's tone generator, do you mean set the RMS output level to -3dBFS? What is the significance of -3dB?
- If, as per your example, -8 for the AVR sub trim is the point where clipping starts, and then you run Audyssey and it sets the trims to -3, you recommend adjusting the sub gains lower, then repeating the Audyssey calibration until the trim set by Audyssey is -8 (or lower). This sounds incredibly time-consuming. It takes an hour to conduct a full Audyssey Pro calibration on my system. When you do this, do you run a quick 1-position Audyssey calibration (using the consumer mic) just to see the trim level Audyssey sets? That would save some time.
- What is not clear to me at this time is what is happening if the MiniDSP is clipping. Does this mean distortion in the sub channel? I'm not sure I would be able to tell whether my sub channel was distorting or not. And once everything is configured per your procedure, what do I look for on the MiniDSP to see if it is clipping or not? The level of the input meter?
- And in a previous post, you mention a sub level of ~72dB, which when all four subs are summed, will result in a level at the MLP of ~75dB. This leads me to believe you are level-matching the subs, not gain-matching. To me, gain-matching involves placing the mic near-field (1-2" from the speaker cone) and setting the gain. This eliminates the effects of the room, which can be significant if you are level-matching with the mic at the MLP. When setting the sub gain using what I call gain-matching, the sub levels are more likely to be in the 85-90dB range, not 72dB. While I am not sure level-matching vs. gain-matching is relevant to the overall procedure, I am curious why you use level-matching.
I appreciate your input. It is important that I get this process nailed down and documented, and I want to make sure what I am doing is correct.