# Searching Equalization That's Digital in / Digital out



## tpointon

This will be a rather longer post to give some background. 

In a nutshell, what I'm seeking is alternatives to the miniDSP DDRC-22D. I have nothing against the DDRC-22D, but usually I like more than one option when considering a purchase.

If you choose to read further, I would appreciate any comments on what I'm about to say. I need to know that I'm getting this more or less right and where there might be weak points in my pursuit of audiophile music reproduction on a Honda Civic budget.

My 2.1 audio setup has a NAD C390DD 'all-digital' amp at it's core. The signal path I'm currently using is:

Digital source > Raspberry Pi w/ MusicBox > HiFiBerry Digi+ > MiniDSP nanoDIGI > NAD C390DD > Axiom M80 x 2 + SVS 12 sub

I've been experimenting with REW to do room EQ with pretty good success. The C390 has 6 EQ filters at fixed frequencies ranging from 40 hz to 240 hz each -12 dB to +4 dB. Using REW, I set those filters as REW specified with a crossover at 70 hz (I think) sweeping 20-300. Then I did a second run of REW to calculate parameters for the nanoDIGI sweeping 80-8000. The nanoDIGI has 5 parametric EQ parameters. I used that sample to generate 4 configs for the nanoDIGI having house curves of -1.8, -2.0, -2.2 and -2.4 dB/octave.

Here's where I've arrived, showing the 2.2 dB/octave setting.








I like what I'm hearing, but I don't have much experience with this room EQ activity. I think if I am to pursue room EQ beyond where I am now, I will need more and/or better matched filter options than I have now.

From what can see, people who've been doing this for years would have been in the analog domain until the equalization stage where they would use say a BFD to go analog-digital_EQ-analog and on to analog amplification.

Obviously with my setup, I stay digital throughout and don't want to (nor can I) drop down to analog just to match the inputs to an EQ.

I think the miniDSP DDRC-22D is one device that would serve. 

Does anyone have *experience with the DDRC-22D* that they would like to share?

Does anyone know of *alternatives to the DDRC-22D*?

Thanks for listening. I look forward to comments.

Happy Holidays All !
Tim


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## AudiocRaver

I have and use the DDRC-22D. I reviewed it and also reviewed the nanoAVR DL. I also have the PC version of Dirac Live.

The digital in/out devices are my own preference for the same reason you have chosen, to avoid unnecessary AtoD and DtoA conversions.

The Emotiva XMC-1 with the +$100 adder for Dirac Live Full, is an alternative, but it is not inexpensive.


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## bertadora

I am using the Behringer DEQ2496 mastering processor that has digital-in and digital-out input/output.

The DEQ2496 has 31 1/3 Oct graphic equalizer and 10 parametric equalizers per channel. 

Both the graphic and parametric equalizers are working in conjunction 

My method is using the REW measurements data to create manually the DEQ2496 graphic and parametric filters the following way:
1.	Equalizing SPL curve to target curve with the 1/3 Octave graphic equalizer
2.	Create narrow (~1/10 Octave) parametric notch filters with the parametric equalizer for suppressing room resonance. 

I achieved excellent sound this way in my small listening room that has some acoustic treatment and its size is 3.3x3.3x2.4 meters (WDH)

See my system layout in below diagram including howto connect the measurement microphone for REW measurements.


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## bertadora

Just adding - in your case you can connect the digital output of the DEQ2496 to your NAD C390DD amp who has optical input.


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## tpointon

bertadora said:


> Just adding - in your case you can connect the digital output of the DEQ2496 to your NAD C390DD amp who has optical input.


Thank you 'bertadora' for that advice. I will certainly look into the DEQ2496.


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## tonyvdb

May I ask why you stuck to using an EQ with digital in outs? If you get a Yamaha YDP 2006 EQ (one of the very best made) and place it just before the amp you will get the same or better results for less money.


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## bertadora

1. The reason to use DEQ2496 Digital out is to be able to use high end D/A (Grace 902) and not to use the internal DEQ2496 D/A that is good but not as Grace 902.
2. The Yamaha YDP 2006 EQ has only 6 parametric EQ per channel vs the DEQ2496 has 10 parametric EQ plus 31 graphic 1/3 octave eq.
I am using all 10 Parametric filters for suppressing my room resonances and the 31 Graphic EQ for SPL to target curve equalization.
The REW has a "find resonances" feature that find the measured room resonances and provide each resonance its center Frequency, it gain and T60 decay value in ms.
See REW help 
http://www.roomeqwizard.com/help/help_en-GB/html/eqwindow.html#top


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## tonyvdb

Not to steer this off topic but it seems that some room treatment would be a better option for you. Using as many filters as you are is not going to give you great results. In my experience the difference in most DAs is negligible.


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## tpointon

tonyvdb said:


> May I ask why you stuck to using an EQ with digital in outs? If you get a Yamaha YDP 2006 EQ (one of the very best made) and place it just before the amp you will get the same or better results for less money.


I'm not sure to whom your question is addressed, but for me the reason I want an all-digital EQ is that I'm arriving at the EQ stage with digital output from the Raspberry Pi and I am needing to feed digital content as input to the NAD C390DD amp. My entire signal path is digital. To quote the description on NAD's website:
Like the M2, the C 390DD has no analogue stages in the signal path, keeping music in the digital domain right up to the speaker outputs.​If Joe Walsh is an 



 I am Digital Man (first worked with a computer in 1967). :whistling: 
.​You are probably right that some room treatment might be warranted. I'm still working to understand my system's interaction with the room.

Tim


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## tonyvdb

tpointon said:


> I'm not sure to whom your question is addressed, but for me the reason I want an all-digital EQ is that I'm arriving at the EQ stage with digital output from the Raspberry Pi and I am needing to feed digital content as input to the NAD C390DD amp. My entire signal path is digital.
> 
> Tim


Weather you keep the signal digital or not is not important if your already analog at the amps inputs putting the EQ just before the amp will give you the same result.


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## AudiocRaver

I believe what the OP is saying, if I understand correctly, is that the path is completely digital up to and into the power amp, which is digital with a digital input, and the power amp output stage itself is the system DAC, the first and only point where the signal changes to analog. And that he would like to accomplish the EQ without adding unnecessary conversion stages.

It can be argued that added conversion stages could probably not be detected audibly. He simply does not want them. In his shoes, I might do the same. Sometimes we make a purist choice like that on principle. Would he hear those extra conversions? Highly doubtful. But if they are not even in the system, then he will definitely not hear them.

The suggestion has been made that room treatment would probably make highly audible improvement in the sound at a fraction of the cost. This is no doubt the case, and remains a suggestion for the OP to consider along with the room correction that he chooses.


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## bertadora

In a small listening room with size of 3.3x3.3x2.4 meters (WDH) there is a space and aesthetic limitationד of how much acoustic treatment you can apply.
I have absorbents and bass traps in the room, it improves the sound but not solving completely the problem of room resonance and early reflations. 
The DEQ2496 with filters created from REW measurements provide a full solution in listening position together with the acoustic treatment. .


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## tpointon

tonyvdb said:


> Weather you keep the signal digital or not is not important if your already analog at the amps inputs putting the EQ just before the amp will give you the same result.


I don't think you're getting the point ... my 'amp' is actually an integrated DAC/amplifier. Even the amplifier section is digital. E.g. when I adjust volume, it is done in the digital domain. The 'amp' has no / zero analog inputs and the only analog outputs are the speaker terminals. Here's a pic of the rear of the amp.






The RCA plugs are SPDIF input/output and sub out. Equalization has to happen inside the box or in the digital domain before the box. That is why, I assume, NAD includes Room EQ adjustments within the amp at 20/40/90/120/180/240 hz. Each of these points can be adjusted -12 db to +4 db and either "wide" or "narrow".

As I said in my original message, I am liking what I'm hearing, but I don't have much to compare with. I am still learning about room EQ and REW. 

My question about all-digital EQ devices was simply to gather information about alternatives. Two replies so far have provided suitable alternatives; the miniDSP device and the Behringer.


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## tpointon

Wayne, you are correct in all you say.

Perhaps a bit of history can illuminate my situation. When I heard my first CD in about 1983, I decided that was it for analog for me No more ticks and pops despite all my caution with discwasher cleaning and keeping LP's in their sleeves. I kept my LPs, but bought CDs thereafter.

Until about 2 years ago, I had a NAD 7000 playing CDs and driving my Axiom M80's. Then a friend mentioned FLAC files and DAC's and that started me down a new path. I ripped all my CDs onto a NAS using JRiver media center on a PC. And I began to purchase High-res music downloads and look at streaming.

But to play this content, I needed a DAC. My NAD 7000 was also a bit long in the tooth by this time. As I looked at DACs, it became apparent that I was going to need to spend significant dollars. (Significant for me would be about $500+. I cannot even contemplate $10k speakers). 

While researching DACs I came upon the NAD C3990DD and ultimately walked into the local dealership and told him to order me one. I don't think he knew exactly what I was getting, but it arrived.

I don't regret my purchase. The performance of the C390 is flawless. But it is true that with it I have the same disadvantage that comes with integrated amplifiers ... I cannot get into the DAC-Amp connection because it's inside the amp. 

NAD provides EQ adjustments in the C390 apparently to tune the sub. But that won't let me do things like a house curve or tweak frequencies above 240 hz.

Using the nanoDIGI before the amp to do some EQ and adjusting EQ within the amp I have a pretty decent sound I believe. But I don't know how to determine that I have reached the best sound I can get. I have never had opportunity to listen to really high end audio; I simply go by what reviewers say with a grain of salt when it comes to things like interconnects and digital jitter and speaker wire and fancy power cords.

Tim


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## tpointon

There seems to be a lot of comments on the Internet about the DEQ2496 overheating. Have you had issues with this? Did you add heatsinks for example?


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## AudiocRaver

tpointon said:


> I simply go by what reviewers say with a grain of salt when it comes to things like interconnects and digital jitter and speaker wire and fancy power cords.


Very wise.

I am aware of no economical alternatives to the miniDSP units for DSP / room correction / Dirac Live. Preamp solutions, like the Emotiva offerings, are great but higher dollar range. For 2-channel, I think the DDRC-22D is your best choice.

miniDSP offers 2 basic Dirac Live engines, the 48 kHz engine in the nanoAVR DL and the 96 kHz engine in the DDRC series.


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## bertadora

I have the DEQ2496 from 2006 and have a friend that has it from 2006 too.
We never had any issue with heating of the unit.
Please note that we use it in listening room as a stand alone unit and not in a hot consul rack with other equipment like high power amplifiers that are running hot and poor ventilation like in DJ or recording studio racks.


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## Wayne A. Pflughaupt

tpointon said:


> I've been experimenting with REW to do room EQ with pretty good success. The C390 has 6 EQ filters at fixed frequencies ranging from 40 hz to 240 hz each -12 dB to +4 dB. Using REW, I set those filters as REW specified with a crossover at 70 hz (I think) sweeping 20-300. Then I did a second run of REW to calculate parameters for the nanoDIGI sweeping 80-8000. The nanoDIGI has 5 parametric EQ parameters. I used that sample to generate 4 configs for the nanoDIGI having house curves of -1.8, -2.0, -2.2 and -2.4 dB/octave.


Since you seem to be into manually setting up your system using REW, I’d agree that the DEQ2496 should be a good option for you to keep a digital signal path up to the amplifiers. I don’t see the point to shell out for the DDRC-22D unless you’re looking to switch to an auto-EQ solution. 

That NAD looks pretty sweet – no doubt what pre-amps and integrated amps will be in the future. :T




tpointon said:


> There seems to be a lot of comments on the Internet about the DEQ2496 overheating. Have you had issues with this? Did you add heatsinks for example?


I’d say look at how their systems are physically set up. If they’re stacking multiple DEQ units, putting them on top of amplifiers or in enclosed racks, that’s probably the problem.

Regards,
Wayne


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## Wayne A. Pflughaupt

bertadora said:


> I am using all 10 Parametric filters for suppressing my room resonances and the 31 Graphic EQ for SPL to target curve equalization.


I’d agree with Tony that you may be over-doing the equalizing. Very few (if any) rooms are ever going to have ten legitimate resonating frequencies. One or two is typical, along with some other peaks and troughs that aren’t true resonances or nulls. No system I’m using YDP2006’s on is using more than 6-7 filters combined for full range (i.e. separate EQs for mains and subs), so 10 filters for the subs alone is - yikes.

I’d suggest reviewing my Minimal EQ article, at least the sections titled “How to recognize useless filters” and the first section of “Tips for those using REW’s auto-EQ function,” which debunks the notion of equalizing for the best time domain results. Sure, it’s just one guy’s opinion, but a good number here have reported back that they got audibly better results “going minimal” compared to their previous tact of EQing to the max. No one has yet to report the reverse, that they got better results plastering their sub with multitude of filters compared to general smoothing.

Regards, 
Wayne


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## AudiocRaver

One more vote for minimal EQ. Ditch the graphic, minimize the parametric, or go with just 3 or 4 parametric - on the worst peaks - plus Dirac Live


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## tpointon

tonyvdb said:


> Not to steer this off topic but it seems that some room treatment would be a better option for you. Using as many filters as you are is not going to give you great results. In my experience the difference in most DAs is negligible.


Thanks, Tony. I will seriously take your advice into account. 

Here's a little anecdote that emphasizes what you say. At one point I was trying out a listening position in my room. I could not seem to get the image to be centered ... everything seemed shifted right, at times further right than my right speaker. I began to wonder if I had a bad speaker so I switched L-R and tried a few other things. But there were no hardware problems. There is a patio door on the right wall of the (small-ish) room that has no window covering. I was sitting where a clear reflection was coming off that glass!


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## bertadora

Hi Wayne,
Regarding over equalizing, please note that I am doing full range equalization with floor standing speakers that goes down to 28Hz, I have a REL Storm III that I used before with my old speakers that went down to 45Hz. Currently the Sub-woofer is disconnected, I may consider later to ingrate it to my system to cover the range of 18-28Hz. 
I am using the DEQ2496 parametric equalizer for creating both narrow notch filters to suppress room resonances and for smoothing the SPL curve for cases that needs narrower than 1/3oct bandwidth peaks that can not be treated with the 31 1/3oct graphic equalizer of the DEQ2496. 

My listening room 3.3x3.3x2.4 (WDH) meters and its treated with Bass traps and absorption panels
Please see below predicted room resonance of my room from REW room simulation. 








My goal is to suppress and bring them below ~300ms RT60 with priority to low frequency resonances, high gain and high RT60 resonances. 
The parametric of the DEQ 2496 has 10 filters and should be used wisely to suppress both room resonances and for smoothing the SPL curve for cases that needs smaller than 1/3oct bandwidth peaks
see below my room SPL curve with DEQ2496 on "bypass" no equlization (Boomy bass, no High roll-off, bad sound)







See my room resonances with DEQ2496 on "bypass" 









The DEQ2496 set manually using REW analysis data resolves most sound problems both resonances and SPL curve. 

I can create a step by step procedure of how to use REW to manually set DEQ2496 GEQ (Graphic Equalizer) and its PEQ (Parametric equalizer) to achieve smooth SPL with roll-off and suppress room modes with narrow 1/10 Oct bandwidth and post it in REW and Equalizer forms for anyone that has DEQ2496 and wants to try my method. 

Your feedback will be much appreciated
Regards 
Issi (bertadora)


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## tpointon

It seems I started a lively conversation here. Thanks to everyone who contributed such useful advice!

For the immediate future, I have decided to concentrate on room treatments and working with the equipment I have.

My plan:

I have a laptop on which JRiver Media Center is running legitimately. When I started using it, I didn't want to dedicate my laptop to the listening room. That was a significant reason for my looking into the Raspberry Pi. 

Recently I bought a used laptop to run Ubuntu Linux and see if I can work mostly with Linux, a browser (Firefox) and my data in 'the cloud'. I'm no fan of Windows.

So I moved my Windows laptop to the listening room to be my HTPC and the Linux laptop to my desk, from which I type as we speak.

JRiver works nicely with my NAD amp via USB for which NAD provides drivers. Also, I think I can work with JRiver to do filtering for house curves etc. A new learning curve, pardon the pun.

Since JRiver doesn't "talk to" Spotify as far as I can tell, I will use my Raspberry Pi to play Spotify. Perhaps at some future time JRiver will work with Spotify (if you know it does already, please tell me how).

Once again, thanks. You guys are awesome helpers. Hopefully I can contribute more in future as I learn more.

Cheers!
Tim


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## bertadora

Hi Tim,
What is the size of your listening room?
Is it rectangular or shoes box type?
Your decision to first improve your room acoustic treatment is the right one.
DSP should be used only after it for additional improvement in the sound.
In my small listening room acoustic treatment helped but only the DEQ2496 made the breakthrough.
Regards,
Issi


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## tpointon

bertadora said:


> Hi Tim,
> What is the size of your listening room?
> Is it rectangular or shoes box type?


My room is 16' 5" x 13' 4" x 8' ( 5.1 x 4.1 x 2.4 metres ) = 1760 cubic feet. Here's the layout in REW Room Sim. There's a fireplace along the front wall that prevents moving the speakers closer together unless I come well into the room.









I've switched to JRiver MC to play music from my NAS through the NAD amp and it sounds very good. I was able to use REW's settings for a house curve to customize JRiver. I'll continue to work in that direction and to read up on and apply room acoustic treatments. 

I appreciate your advice about the DEQ2496 ... if I decide to purchase a DSP, it could well be that one.

Thanks,
Tim


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## Wayne A. Pflughaupt

bertadora said:


> See my room resonances with DEQ2496 on "bypass"


Are you saying that your room resonances are where all the blue pointers are in the top graph?

Regards, 
Wayne


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## bertadora

Hi Wayne,







The arrows up to 200hz are measured room resonance by REW, you can see the measured vs the predicted by REW room simulation. 
The arrows from ~200hz up to 400hz we can relate them as room reverberations with decay above 300ms.
Recommended RT60 for small control/mastering room like my listening room is ~300ms, and it is also the default value in REW for "find resonances"

My goal is to suppress and bring them around ~300ms RT60 with priority with filters selection to low frequency resonances, high gain and high RT60 resonances as number of parametric filters is limited to 10. 

See below spectrogram with DEQ2496 GEQ and PEQ filters "ON" done manually.








Regards,
Issi


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## Wayne A. Pflughaupt

I’m no expert on this subject, but F. Alton Everest’s _Master Handbook of Acoustics_ recommends 400-500 ms as the ideal reverb time for a studio control room, so a target of <300 ms seems pretty optimistic.

For starters, I wouldn’t be equalizing all those little ripples in response above 200 Hz that you’re showing. It isn’t going to give any audible benefits, and can actually be detrimental. Equalizing with filters as fine as the 1/10-octave type your talking about are tight enough to actually _attenuate notes_ of the musical scale, if they happen to hit the fundamental of the note. So for a run of bass notes, for example, you could audibly notice a particular note at a lower volume than those before or after.

Second, if you take additional measurements some months down the road you will find that they are not perfectly identical to the previous ones, and REW will recommend a different set of filters. So – which measurement / recommended filter set is the correct one?

Fourth, it’s pretty well known that equalizers are not the proper tool for addressing acoustical issues. Absorption is the best method for reducing high Q resonances. An equalizer can only reduce the gain of a specific frequency; it has no effect on its decay time (other than what comes normally with a gain reduction). As such equalizers are mainly good only for smoothing peaks and troughs in response.

Again, I recommend reviewing the material mentioned previously in Post #19.

Regards,
Wayne


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## bertadora

Hi Wayne,
I fully agree that first priority is Acoustic treatment that should be done in the small listening room as much as it can with the limitation of space and ascetics.
I am familiar with the F. Alton Everest’s Master Handbook of Acoustics from 1981, I have it and read it all.
I like to refer you to SOS magazine article from PAUL WHITE from 1985 that is title is "PRACTICAL ACOUSTIC TREATMENT" Part 3 https://www.soundonsound.com/sos/sep98/articles/acoustic_3.html

I quote from the T60 section *"The ideal reverb time varies depending on the room size and the type of material being auditioned, though for a control room it's likely to be around 0.3 seconds"*
I like to hear exactly how the material sounded in the control / mastering room. 

Today, many of the young generation are listening to music material through smart phone and tablets and some of them with good quality head phones that does not have a reverberation as in a listening room.

Mastering engineer today have to make sure that the material they produce will sound good on both headphones and in a listening room. The result usually is a compromise with some extra reverb in the recording as there are no different versions published for headphones and listening room. 

I listen to lots of opera material and to get the singers to sound natural the 300ms RT60 in my small room sounds right to me with comparison to high quality headphones.

The DEQ2496 parametric filters (in my case the 1/10 Oct filters) can be activated or deactivate. 
When you detective the PEQ the GEQ that is set with its 1/3oct 31 sliders to target curve equalization is still active.
The real impact of the narrow PEQ filters can be evaluated easily by activating or deactivating the PEQ and listening to many quality recordings (My recommendation - Large drum impacts of symphonic orchestra, Pop music, Jazz, symphonic music, concertos of violin, piano, trumpets...) 
Best regards,
Issi


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## AudiocRaver

I agree that 0.3 seconds is a good T60 for a control room.


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## Audioguy

AudiocRaver said:


> One more vote for minimal EQ. Ditch the graphic, minimize the parametric, or go with just 3 or 4 parametric - on the worst peaks - plus Dirac Live


+1


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