1 Topic by johny_2000 (edited by johny_2000 2024-10-18 06:47:41)

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Topic: Parametric EQ Preamp Gain

Hi all,

I apologize if this has already been discussed somewhere.

In a classic parametric EQ there is a preamp gain setting that provides headroom for any possible gain bands to avoid output clipping. These negative preamp gain values are provided by the people who prepared the special PEQs for the headphones/speakers, software (like REW equalizers) or by the user by looking at the graph, and the maximum combined EQ gain should be below the 0 dbFS line.

I know that RME took this preamp gain into account when implementing parametric EQs in the ADI-2 DAC. But how it works is completely invisible and sometimes it is difficult to predict the output level of the device with PEQs enabled.

For example, I have a bass boost (low shelf) of +6 dB enabled in the parametric EQ for the headphone 3/4 outputs. The graph correctly shows me this gain. But my ADI-2 Remote app output level never changes. If you look at the SOV status of the Phone 3/4, it will be, for example, +7 dBu. No matter what I do with the PEQs/Loudness settings, it always stays at +7 dBu, depending solely on the position of the Volume slider (AutoRef or Manual, same thing).

2 Reply by MC

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Re: Parametric EQ Preamp Gain

Do some more extreme settings like +12 dB and then change volume manually. You will notice that the point of auto-switching the ref levels will have changed.

Regards
Matthias Carstens
RME

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Re: Parametric EQ Preamp Gain

So the EQ preamp gain (negative) is taken into account in AutoRef mode?

I just rarely use AutoRef mode, and prefer to set my reference levels and volume slider manually, confirming the results in the SOV window.

4 Reply by KaiS (edited by KaiS 2024-10-19 09:04:32)

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Re: Parametric EQ Preamp Gain

ADI-2 has an internal headroom of 24 dB for DSP processing.
This means you hardly ever can overload it internally.

If you want to set your own reference level, Watch the Horizontal Meter in setting “Post FX” and dial down the volume control enough to keep the output from clipping.


Or read the chapter about Auto Ref Level in the manual.
You will find that ADI-2 exactly does what you would do anyway, fully automatic.


Excerpts from manual page 39:

The analog outputs also feature a mechanism to set the reference level automatically. Auto Ref Lev(el) maximizes the signal to noise ratio when using the Volume knob. It changes to the next higher and lower reference level setting when the gain chosen via the Volume knob would suggest to set a better fitting value, with optimized signal to noise ratio.

Example: Ref Lev is set to +19 dBu, Volume is turned down to -20 dB. The effective signal to noise ratio at the XLR output is now 120 dB minus 20 dB = 100 dB (RMS unweighted). While it is unlikely that any noise will be audible, changing the Ref Level to +1 dBu would need only a Volume setting of -2 dB to achieve the same level or volume. The effective SNR then becomes 117 minus 2 = 115 dB (15 dB higher). Such settings are usually done manually by the user. Auto Ref Level takes over this task, working in both directions when turning Volume up or down.

Notes on Auto Ref Level:

… To prevent distortion the threshold for a Ref Level change takes EQ gains into account.

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5 Reply by ramses (edited by ramses 2024-10-19 09:21:36)

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Re: Parametric EQ Preamp Gain

johny_2000 wrote:

So the EQ preamp gain (negative) is taken into account in AutoRef mode?

Yes, also dynamic Loudness.

johny_2000 wrote:

I just rarely use AutoRef mode, and prefer to set my reference levels and volume slider manually, confirming the results in the SOV window.

Why? Auto Ref Level is a very useful feature. I know exactly when my preamp starts clipping, so I avoid setting levels too high. Just like with any volume control (radio, TV) – if it's too loud, you turn it down.

Simply put, Auto Ref Level automatically selects the most suitable level to maximize SNR and dynamic range by making optimal use of the 4 (or 5 with the 2/4 Pro SE) reference levels.

This Excel sheet shows the benefits across all reference converters: it illustrates the range where you get higher SNR and when the level switches (excluding EQ and dynamic loudness):

https://www.tonstudio-forum.de/attachme … v004-xlsx/

And really the best is, that B/T, PEQ and dynamic loudness settings are also taken into account for the automatic switching of ref levels.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13
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Re: Parametric EQ Preamp Gain

KaiS wrote:

ADI-2 has an internal headroom of 24 dB for DSP processing.
This means you hardly ever can overload it internally.

Oh, 24 dB is a lot of headroom. My EQs don't go over +6-7 dB, and the Loudness feature set to +6 / +4 / -30 dB. Hopefully it won't exceed the DSP headroom without using AutoRef mode. But I'll have to test that mode because it seems to have some benefits.

7 Reply by MC

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Re: Parametric EQ Preamp Gain

If so you would see it in the level meters. For manual operation point is you simply turn down the output volume and overload is gone.

Regards
Matthias Carstens
RME

MC's Website

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Re: Parametric EQ Preamp Gain

ramses wrote:

Why? Auto Ref Level is a very useful feature.

Thanks!

I used the AutoRef feature today for the XLR outputs and was surprised that the logic behind it kept the Ref level at +13 dB when the output volume was set to +1 dBU (SOV). Until I turned off the parametric EQ (1st click or relay) and Loudness (2nd click of relay) at which point the Ref level went to +1 dB.

It seemed to me that it maintained 12dB of headroom when I used the 6dB max EQ and 6dB max Loudness features.

9 Reply by KaiS (edited by KaiS Today 11:13:13)

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Re: Parametric EQ Preamp Gain

johny_2000 wrote:
ramses wrote:

Why? Auto Ref Level is a very useful feature.

Thanks!

I used the AutoRef feature today for the XLR outputs and was surprised that the logic behind it kept the Ref level at +13 dB when the output volume was set to +1 dBU (SOV). Until I turned off the parametric EQ (1st click or relay) and Loudness (2nd click of relay) at which point the Ref level went to +1 dB.

It seemed to me that it maintained 12dB of headroom when I used the 6dB max EQ and 6dB max Loudness features.

With Auto Ref Level on, the Volume is displayed in dBr.
This “r” means the dB value is referenced to ADI-2’s 0 dB volume setting at highest reference level.
DSP effects like EQ and Loudness are considered in the dBr calculation.
This gives a clear indication of the real output level control position.

The meters set to “Post FX” will show real DAC usage before analog reference level switching.
They typically stay peaking between -6 dB and full (meaning good usage of DAC’s dynamic range) until volume is dialed down below ca. -20 dBr.
Somewhere around this point lowest analog ref level is reached.

BTW: The DAC has a headroom of 2.5 dB above “Over”-indication, so a little “red” on the meters doesn’t hurt in this case.

The beauty of Auto Ref Level is, that digital volume control and analog ref level switching works hand-in-hand for a seamless continuous volume control, maintaining ADI-2’s high dynamic range even when volume is dialed down.

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