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TOPIC: Gain and preventing clipping

Gain and preventing clipping 3 months 1 week ago #48118

  • Tony_J
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Ultrasonic wrote:
Tony_J wrote:
devteam wrote:

Mmh i guess that our long explanation above maybe didn't get through.. :-( Not sure what else we can explain here that Dirac will add some boosting to match the target curve. Would you agree to that step#1? If not we've got a problem.. ;-)

Step#2, your REW is completely different from Dirac Live. So you can't compare the amount of correction between these 2 method. Would you agree?

Step#3. Somewhere, you need to attenuate the signal. We recommend to keep some headroom e.g. -6dB is good. By default, Dirac recommend -10dB. (i.e. max attenuation)

If our suggestion to say add -5dB as safety isn't acceptable, maybe you could try to see the before and after on Dirac to try to guesstimate the amount of attenuation? Or just go -10dB and you'd be safe at all times.



Mmmh indeed. I guess you didn't read what I wrote because if you had, it would be clear to you that yes, I agree with your step #1 - Dirac is clearly applying a boost to some frequencies to match the target curve. My point is that the *amount* of boost that it applies isn't readily obvious to the user, and therefore, any corresponding cut that the user needs to apply in order to avoid clipping has to be made on a trial-and-error basis. Dirac *could* provide precise information on this - for a given set of filters that its calibration tool generates, they *absolutely could* report the max boost that it can generate. That would then allow me as a user to give precisely the right amount of headroom rather than doing a trial - and - error exercise, and still not knowing whether I had really left enough headroom.

Failing that, there *absolutely should* be a clear statement in your product documentation that the Dirac algorithms can generate a boost of up to (x) dB - at present, that *is not* stated in your product documentation for DDRC-24, which I believe is a serious omission. The reason that I say it is a serious omission is from personal experience - when I heard the consequences of failing to provide the necessary headroom, my first reaction was "what a piece of c*** - this product is rubbish". I read the DDRC user manual, and it gave me no help whatever; it was only when I started trawling the posts in the forum that I figured out what was going on and what the fix was. You mention above that " By default, Dirac recommend -10dB" - that's all very well, and potentially useful information, but it certainly isn't mentioned in the DDRC-24 documentation, so where does that information come from exactly? I don't doubt its accuracy, I just don't understand why it isn't written in the DDRC-24 manual.

You discuss the topic of "gain structure" in the product documentation (and this applies equally to the 2X4 HD manual), but this discussion relates ONLY to the gain structure outside the digital domain. You really do need to mention gain structure as it applies to the operation of your hardware. This may seem obvious to you, and it is obvious to me *now*, having gone through a lot of reading and searching, and having been on the point of binning the hardware at one point, but you could save your users a lot of time and effort (and potential disappointment) by addressing the topic in the user manuals. For example, you should point out *at least* the following:

- If the signal applied to the analogue inputs exceeds 4v or 2v RMS, then the ADC will clip.
- Internally, there is no heardoom issue for practical purposes (I read elsewhere in the forum that the headroom is at least 100 dB internally, because the hardware uses 32 bit arithmetic).
- If any filter elements that are applied in the digital domain can result in any part of the digital signal being boosted above 0dB, then it is essential to apply a corresponding overall level cut before outputting to the DAC, otherwise the resultant analog signal will exhibit clipping (i.e., any part of the waveform that cannot be represented in 24 bits is truncated to 24 bits).

It would also be helpful to the user to understand that the RMS meters in the plugin show the level *after* any analogue signal has been through the ADC (in the case of the meters on the inputs) and *immediately before* the signal is output to the DAC (in the case of the meters on the outputs), and therefore, if you see the output levels peaking in the positive dB range, then you haven't applied enough of a cut.

It is a shame that the above post has seemingly been ignored so far by @devteam but I thought I'd bump this as the points raised still seem completely valid. I came across this post having started to experiment with Dirac on my SHD, and trying to find information of how to make sure digital clipping is avoided.

I've done a bit more work on this - see: www.minidsp.com/forum/dirac-series-suppo...ernal-headroom#48111
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