1 Topic by skyfly (edited by skyfly 2021-12-08 14:16:54)

  • Registered: 2021-12-02
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Topic: clipping due to EQing, how is it prevented?

This may be a novice question. Anyway, I think the peak level of the signal may increase by EQing, either by boosting or cutting some frequency. (For example, consider a square signal and its Fourier series. If we cut the third harmonic, the peak level becomes higher.)

I remember that analog pro EQ gears have a clipping indicator and a level control.

How is the clipping prevented in the digital parametric EQ in RME ADI-2? I do not see signal level control.

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Re: clipping due to EQing, how is it prevented?

An EQ is basically a volume controll for selected frequenzies. So youre overall level is to high. Set down youre reference level to make more headroom.

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3 Reply by ning (edited by ning 2021-12-08 15:24:03)

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Re: clipping due to EQing, how is it prevented?

There are two different things.

1. Let’s say you are at volume 0dbfs and you have a signal that is -5dbfs. You boost that by 10db then it’s at 5dbfs. It’s certainly clipping in this situation as the dac chip cannot output higher than 2.5dbfs. You will clearly see in the screen’s level meter it’s clipping.

2. You are at a low volume. Say -15dbfs. You boost a 1khz -5dbfs signal by 10db. Then it’s at -10db and it won’t clip at all in analog.

The latter does need to do calculation carefully because although it’s -5+10-15, digitally it clips when you calculate -5+10 if you use the same calculation range as the signal. That’s why RME uses a much larger range (48bits integer range vs 32 bits signal level range) when doing dsp

(In this simplified case it’s true that by -15-5+10 you can avoid the overflow issue. But in real world you are not always that fortunate. So it still serves as a good demonstration on various scenarios it can overflow if you use the same bit length.)

4 Reply by 04gto (edited by 04gto 2021-12-08 15:17:57)

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Re: clipping due to EQing, how is it prevented?

@Skyfly- Did your unit come with a manual? The manual is perhaps the best manual to come with any piece of gear I have ever owned. You should read/study it thoroughly. This question and many others will be answered in the 70 pages of English or German, wwenn du deutsch bevorzugst.

5 Reply by KaiS (edited by KaiS 2021-12-08 18:52:48)

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Re: clipping due to EQing, how is it prevented?

skyfly wrote:

How is the clipping prevented in the digital parametric EQ in RME ADI-2? I do not see signal level control.

Simply by 24 dB internal headroom.
Look at manual page 25.

I.e. you boost the bass by 12 dB, then dial back the Volume by 12 + a little dB.
Switch on “Auto Reference Level” (factory default = On), then the dBr value of the volume control shows how much control range is left.

“Auto Reference Level” cares for optimized levels matching.

Without “Auto Reference Level” you would need to keep an eye on the Output Level Meters.

KaiS's Website

  • Registered: 2021-12-02
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Re: clipping due to EQing, how is it prevented?

This is my understanding.
My calculation may be off by 0.5 dB, but that is not a big concern here.

With Auto Reference Level on
and at the volume level -18.5 dBr, -12.5 dBr, -6.5 dBr, and -0.5 dBr,

there is a digital headroom of merely 2.5 dB in the ESS DAC chip.

With Auto Reference Level on
and at the volume level -24.0 dBr, -18.0 dBr, -12.0 dBr, and -6.0 dBr,

there is a digital headroom of merely 8.5 dB in the ESS DAC chip.

https://lh3.googleusercontent.com/pw/AM-JKLUEACxEh-xPRp3Q-mQCcMHtAr_dN1WPIw8gQT0ew6LimEv4C9O9JoTclyCSGx9mUWhFgQeHoHXsFCQpMOHWqSrQlAHj46xqmKvCdglnjssFRgEiRMsBDW2o1EwMwYVKUOaHHvFFC4Yr_q6q8k5B1bnJ=w2840-h2007-no?authuser=0

Hence, even though the digital EQ has 24 dB internal headroom, there can be clipping at the ESS DAC chip at a volume level near -18.5 dBr or above.

  • From: Hongkong
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Re: clipping due to EQing, how is it prevented?

Read page 25 of the user manual PLEASE.

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Re: clipping due to EQing, how is it prevented?

KaiS wrote:
skyfly wrote:

How is the clipping prevented in the digital parametric EQ in RME ADI-2? I do not see signal level control.

Simply by 24 dB internal headroom.
Look at manual page 25.

I.e. you boost the bass by 12 dB, then dial back the Volume by 12 + a little dB.
Switch on “Auto Reference Level” (factory default = On), then the dBr value of the volume control shows how much control range is left.

“Auto Reference Level” cares for optimized levels matching.

Without “Auto Reference Level” you would need to keep an eye on the Output Level Meters.

The dual meters also helps.

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9 Reply by KaiS (edited by KaiS 2021-12-09 08:53:26)

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Re: clipping due to EQing, how is it prevented?

skyfly wrote:

This is my understanding.
My calculation may be off by 0.5 dB, but that is not a big concern here.

With Auto Reference Level on
and at the volume level -18.5 dBr, -12.5 dBr, -6.5 dBr, and -0.5 dBr,

there is a digital headroom of merely 2.5 dB in the ESS DAC chip.

With Auto Reference Level on
and at the volume level -24.0 dBr, -18.0 dBr, -12.0 dBr, and -6.0 dBr,

there is a digital headroom of merely 8.5 dB in the ESS DAC chip.

https://lh3.googleusercontent.com/pw/AM-JKLUEACxEh-xPRp3Q-mQCcMHtAr_dN1WPIw8gQT0ew6LimEv4C9O9JoTclyCSGx9mUWhFgQeHoHXsFCQpMOHWqSrQlAHj46xqmKvCdglnjssFRgEiRMsBDW2o1EwMwYVKUOaHHvFFC4Yr_q6q8k5B1bnJ=w2840-h2007-no?authuser=0

Hence, even though the digital EQ has 24 dB internal headroom, there can be clipping at the ESS DAC chip at a volume level near -18.5 dBr or above.

The 24 dB is an INTERNAL headroom to avoid INTERNAL clipping.
The DAC chips work with less, the real DA conversion without headroom.

“Auto Reference Level” is related to the maximum ANALOG OUTPUT level.
As ADI-2’s Volume control happens in the digital domain, it’s “Auto Reference Level”  works as a combination of ANALOG gain staging (by analog hardware switching with relays) and digital volume control.

The dBr value is in fact the possible control range available.

The digital headroom you calculated is of interest with “Auto Reference Level”  off only, if you manually set the analog Reference Level.
With “Auto Reference Level”  “OFF” you don’t see dBr anymore, just plain dB in the Volume control.

KaiS's Website

10 Reply by skyfly (edited by skyfly 2021-12-09 09:47:35)

  • Registered: 2021-12-02
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Re: clipping due to EQing, how is it prevented?

I thought I was one of technics/measurement oriented hi-fi users, but I need to seriously study the features of RME ADI-2.

It seems that the parametric EQ in RME ADI-2 automatically adjusts what corresponds to the level control on the analog EQ gears. The RME ADI-2 seems to automatically (according to the EQ setting) perform volume-down within the digital EQ to reduce the chance of clipping and also volume-up in the the 4-stepped analog gain control after the DAC chip.

I just boosted bass (+12 dB, 90Hz, Q 0.5) in the parametric EQ, and am playing 0 dBFS 50 Hz track.

[with EQ off]
L: -1.8 (-1.8 with 1 kHz 0 dBFS track)
R: -1.8 (-1.8 with 1 kHz 0 dBFS track)
VOL -18.5 dBr
-5 dBu (Auto)

[with EQ on]
L: -4.8 (-13.7 with 1 kHz 0 dBFS track)
R: -4.8 (-13.7 with 1 kHz 0 dBFS track)
VOL -18.5 dBr
+7 dBu (Auto)

Whenever I turn on or off the EQ, I hear clicking sound from the change of analog gain after the ESS DAC chip.



P.S.: I am starting to like the 4-stepped analog gain control after the DAC chip in ADI-2. Theoretically, it is a feature for conveniently achieving high signal to noise ratio in audio frequency band. In practice, however, the circuit becomes more complicated and may result in poor sound quality if poorly implemented. The sound quality of RME ADI-2 (compared to a DAC with single fixed analog output level) is good to my ears (Sorry for talking about a subjective feeling.).

Correction:
According to MT, AutoRef takes B/T(bass/treble) and EQ into account and changes the level to prevent clipping.

11 Reply by KaiS (edited by KaiS 2021-12-09 09:29:05)

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Re: clipping due to EQing, how is it prevented?

It’s not too complicated if you’re familiar with gain staging and digital audio formats.

Think of the ADI-2 as blocks:
• Digital Input (no headroom)
• Optional Sample Rate Converter (3-6 dB adjustable headroom)
• Digital Processing and Volume Control (24 dB headroom)
• DA-Conversion, digital part (no headroom)
• DAC chip’s analog stage (ca. 3 dB headroom)
• ADI-2’s analog output amplifier (DAC 18 dB, Pro 20 dB mechanical relay stepped gain staging)

Practically the “Auto Reference Level” function does all necessary calculations and adjustments (digital volume and analog reference level) for you, so you just don’t need to care.

KaiS's Website

12 Reply by MC

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Re: clipping due to EQing, how is it prevented?

The PEQ doesn't adjust volume. AutoRef does, it takes B/T and EQ into account and changes the RefLevel to prevent clipping.

Also, you think too much wink

The unit has all the headroom it needs. With AutoRef off it is you who prevents clipping, by looking at the Post FX (default) level meters and reducing volume to get the levels down. In real-world this hardly happens as volume is dialed down anyway.

Regards
Matthias Carstens
RME

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  • From: Hongkong
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Re: clipping due to EQing, how is it prevented?

At user manual page 66, the block diagram gave you an idea how it works.

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  • Registered: 2021-12-02
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Re: clipping due to EQing, how is it prevented?

Thanks to all.

It is good to learn that, with the Auto Ref Level feature on, the RME ADI-2 unit takes B/T and EQ into account and adjusts the level in digital and analog domain to prevent clipping while maintaining high SNR, and thus I do not need to worry about clipping from using the digital domain tone control or EQ.