TOPIC: Gain and preventing clipping

Hi,

the Dirac Live Calibration Tool has a slider "Output volume" in the last tab. Is there any risk setting it to maximum? I guess a boost in the equalisation would clip the output? Also how is it related to the output volume in the DDRC24 plugin?

Thanks

@sladi

In a typical setup, I don't think we've seen a time where you'd run this fader @ 100%... (maybe based on our gain structure).
WIth this said, you're correct. Best to keep some headroom here to say -10dB just in case.

DevTeam

I really would want some kind of clip detection implemented. When i set to -10db I get a bit too low output from my DAC (after a DDRC-22D).

@aronake

Wouldn't there be some amplifier post you DAC where you can easily tweak that dip in level? i.e. just increase the volume of your amplifier to catch up that level decrease required we can boost levels inside Dirac.

Wouldn't there be another setting than -10dB ? I believe there is a -3dB as well.

DevTeam

@devteam: There is a slider, -10dB, -3dB are possible, or anything else in between for example.

As far as I see, as a user I would like to set this slider so that the maximum boost created by the Dirac EQ is shown. For example, if it is +5dB, then I know that I could set the output level to -5dB to ensure that there is no clipping.

sladi wrote:
That would be very useful indeed, then you would have a much more accurate guide to the attenuation (if any) that you need.

As far as I can see, that slider only affects the setting of the "Master Volume" in the DDRC-24 - which can be overridden, potentially with unpleasant-sounding consequences, either by means of the remote volume control or the Master Volume box in the plugin. Wouldn't it be more sensible for this to be reflected in the gain settings for the Dirac 1 and Dirac 2 inputs instead? Or even better, have the option of making it a fixed max value for the Master Volume?

...also, the slider is pretty finicky to use; it would be helpful as well as the slider to have a box where you could enter a dfinite value.

@devteam Any comments from the dev team...?

Dear Both

I think that there is a bit of a misunderstand as to what we're talking about here. Some of you are also mixing platform. i.e. DDRC-24 does not working like a DDRC-22D. The attenuation we talked about only applies in the DDRC-22 utility.

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So I clarify it, here is the concept for the DDRC-22.

- "Before" applying Dirac Live, Dirac research recommend DSP to apply to attenuation to the DSP chain so their algorithm has enough "headroom" to apply EQ to the measurement. That attenuation can be set as -10/-3/0dB as per the manual. There isn't any reason for any other settings really. -10dB is what we'd recommend

- The "master" volume is completely different (completely unrelated). It's in the DSP chain at the end and available in 0.5dB increment from the front panel. You can control the volume as much as you want there.

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The DDRC-24 is different (not default attenuation control. You would do it from the OUTPUTS and LEVELS page. It's the INPUT attenuation on the DDRC-24 plugin.
Our recommend is just to not set that level too high or too low. Dirac Live will adjust afterward to level align (so you don't need to have accurate values). We unfortunately have zero control over the GUI of Dirac.

The "Master output Volume" at the top of the GUI (and in the as the Master volume inside DDRC_24) is exactly the same as your master volume control (full control over IR or from the GUI). That won't happen to clip. You don't have to worry about this. You can see the master volume in the top right of the plugin. As per our manual, when you drag a dirac live filter into the slot, you can indeed increase the volume slowly. It's low by default for safety.

Does this make any sense?

Devteam

Thanks @Devteam - that makes good sense.
However...let me describe the problem I am experiencing with my DDRC-24.

I had previously used it as a miniDSP 2x4HD and have since upgraded. Before the upgrade, I habitually used the 2x4HD on maximum "Master Volume" (0dB) as its output feeds a passive preamp with its own volume control. I have never had any "clipping" problems with the signal in that setup.

Since the upgrade to DDRC-24, and again, with the Master Volume set to 0dB, for most of the music I play, there is no problem; however, I have noticed one or two tracks where in particular, female vocals became distorted and harsh. Dropping the MasterVolume by 5dB completely fixes this problem, even with the volume on the passive preamp set much higher than it was when clipping was noticed; this can only be happening because there is clipping in the digital processing (not in the subsequent amplification chain) because the effect is also audible with the volume control on the preamp set very low (9 o'clock on the dial).

Hence my agreement with the comments above that it would be useful to know what is the max level of boost that Dirac has applied in order to achieve a given filter profile; if I knew that, I would be able to fix Master Volume at exactly the level needed to make sure that the Dirac filters have enough headroom.

And having a fixed max on the Master Volume actually wouldn't affect the Dirac software at all - that part of the interface is in your DDRC-24 plugin, which I presume you are in control of.

Tony_J wrote:
@Devteam - any views on this?

@Tony_J

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.

devTeam

devteam wrote:
@devTeam

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.

My initial description was a bit confusing, but I agree with Tony_J and I believe that it should be clear now.
The screen inside the Dirac Tool, where you set the output level, should warn the user when they do not leave enough headroom for the Dirac filter boost. Maybe the Dirac filter does not provide the information (just visually in the filter screen), that would be unfortunate. I guess Dirac should know internally at least the maximum boost that is applied.