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TOPIC: DDRC-24 gain structure and internal headroom

DDRC-24 gain structure and internal headroom 3 months 1 week ago #48297

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Wanderer wrote:
The response based on combined L+R measurements may have nothing in common with individual channel filters.

Yes but I'm not sure what a combined left and right measurement would have to do with the current discussion? The aim here is to measure each of the Dirac filters individually. You'd want to know the highest boost in either filter.

I essentially never make a combined measurement actually as they're of no use to me, since I use a mono bass signal below about 100 Hz.
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DDRC-24 gain structure and internal headroom 3 months 1 week ago #48299

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Tony_J wrote:
On the convenience issue, I think it is a case of six of one and half a dozen of the other. My original approach (do a sweep and spot the peaks/values on the DDRC peak meters) is actually pretty easy and quick to do, and my subsequent more critical measurements seem to validate that approach as long as you then round up the biggest peak value (see my most recent post above). To me, that is much easier and les prone to misinterpretation than doing two sweeps in REW and dividing one by the other, and then worrying about which parts of the resultant curve you need to ignore because of measurement artefacts. It also works for the whole of the audio range.

I hadn't appreciated that you were able to use a slow sweep to be able to look for peaks by looking at the meters. This does make your approach more usable.

If people are just interested in the sub-200 Hz region (as I am currently) I still think the measurement approach is the easiest, most informative (gives the full picture and phase info.), and I really don't think is limited on the accuracy front by any meaningful extent. I would be interested in your comparison if you left the room for the measurements as this may be a factor in the remaining differences shown in the table above. I may try to have a play with this myself at some point as I'm struggling with why the results don't match better if not.

It may just be me but I always like to make a comparison measurement of results with and without the filter anyway to see what is actually going on.

I still suspect the max. boost is always 10 dB though and so this can just be used as a basis of any attenuation applied to prevent digital clipping.
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DDRC-24 gain structure and internal headroom 3 months 1 week ago #48300

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Wanderer wrote:
I don't have specific knowledge about room non-linearity, but guess you are right that it should be a minor factor when the dynamic range is small. (Although, even ±10 dB is actually a huge variation if you convert it from dB to linear scale.)

True. The whole premise of Dirac Live working would fall apart if there were significant non-linearities over such a range though, as the applied corrections then wouldn't get close to doing what the calculations had assumed/predicted.

Thinking about it I have done some compression tests on an old subwoofer which show pretty good linearity actually. Below is an example, where the shape of the curves really is pretty consistent over a 35 dB range of drive signal.


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Last Edit: 3 months 1 week ago by Ultrasonic.
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DDRC-24 gain structure and internal headroom 3 months 1 week ago #48305

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Ultrasonic wrote:
Yes but I'm not sure what a combined left and right measurement would have to do with the current discussion?
Nothing at all... Sorry, I wasn't thinking clearly. Need to sleep a bit more :)

Ultrasonic wrote:
Below is an example, where the shape of the curves really is pretty consistent over a 35 dB range of drive signal.
That is a comforting result, thanks for testing.
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