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My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration

70.32.0.103
Posted on March 17, 2019 at 16:15:16
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011



I recently purchased the Minidsp NanoDIGI which is an all digital solution with one SPDIF/TOSLINK IN and 4 SPDIF outputs. With this solution one can use their own ADC and DAC to surround the NanoDIGI for a potentially more high end solution. Also with 4 SPDIF outputs, the nanoDIGI can support a 2 way active crossover plus 4 subwoofer integration all in the digital domain.

Reference Posts:

1. My Magnepan 1.6QR DIY Upgrade Story (OEM crossover upgraded parts)
http://db.audioasylum.com/mhtml/m.html?forum=mug&n=171078

2. My Magnepan 1.6QR DIY Upgrade II: Going Active!!
http://db.audioasylum.com/mhtml/m.html?forum=mug&n=184970

3. My Magnepan 1.6QR DIY Upgrade III: Going PLLXO!!
https://www.audioasylum.com/messages/MUG/196102/

4. Bringing the HSU TN1220's into the modern era!
http://forum.hsuresearch.com/showthread.php?t=95245

I feel like I am going backwards and forwards at the same time. With this upgrade I am in some sense returning to my Minidsp based solution. I was never completely happy with the Minidsp 2x4 solution since it relied on the built in ADC and DAC in the minidsp box. Now with the nanoDIGI I have a chance to go back to the DSP world for another try at an active crossover design.

Reference #1 above to see how to bypass the factory crossover to attach your power amps directly to the Magnepan 1.6 Tweeter and Woofer panels.

Reference #2 above to see how to setup the Minidsp DSP filters to emulate the factory Magnepan 1.6 crossover.

Reference #4 above to see how to emulate the HSU TN1220 Bass Optimizer box with Minidsp filters.

Here are some of the software and hardware choices in my solution:

MiniDSP nanoDIGI 2x8
https://www.minidsp.com/products/minidsp-in-a-box/nanodigi-2x8-b

SMSL M8 DAC
https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-smsl-m8-dac.2457/

Focusrite Scarlett 6i6 2nd Gen
https://focusrite.com/usb-audio-interface/scarlett/scarlett-6i6

Jriver Mediacenter Software
https://jriver.com/

Plus Parasound HCA-1000A poweramps, Crown Drivecore XLS-1000 and XLS-1500 poweramps, HSU TN1220 subwoofers (2), SVS SB-1000 subwoofers (2). Firestone Audio Bravo USB/SPDIF reclocker adapter.

Here are some of my Design Choices and Relevant Discussions:

1. MiniDSP nanoDIGI 2x8. I considered the MiniDSP SHD which combines many of the functions I am implementing here all in one box. However, since I already had the Focusrite, SMSL DAC's and audioprocessor PC with jriver, I decided to roll my own solution. The nanoDIGI can support IIR filters (it is not powerful enough for DIRAC or FIR filters). If I in the future goto FIR filters I can implement them in the audioPC with jriver and rephase. The nanoDIGI has an IR receiver and can switch between TOSLINK and SPDIF inputs via a IR remote signal. I am using this to switch between "Music" mode and "HT Bypass" mode. With the nanoDIGI I am able to implement the Magnepan crossover, HSU Bass Optimizer filters and the mains/subs integration/time align all in the digital domain. I was able to use the nanoDIGI delay function to adjust for the fact that my 4 subwoofers have different distances to my Main Listening Position (MLP). I was also able to implement a high pass filter on the woofer panel of the Magnepan's to offload the below 45 hz signal.

2. Jriver Media Center. Jriver supports DLNA and FIR filters via rephase. Jriver also has a 64bit math engine to support resampling of the bitstream to 24/96k which is the internal processing rate for the nanoDIGI. By converting all of the PCM audio to 24/96k before it gets to the nanoDIGI I can avoid the (potentially) lower quality ASRC function of the nanoDIGI. When operating my solution in "Music" mode, I am using the jriver software to implement volume control. The jriver WDM function allows me to pass all of the spotify music thru the jriver 64 bit engine prior to sending it on to the nanoDIGI.

3. Focusrite Scarlett USB ADC/DAC. The Focusrite supports 6 IN and 6 OUT. 4 Analog XLR plus 2 Digital SPDIF Inputs and Outputs. The Focusrite processes at 24/192k and has relatively high quality ADC and DAC inputs/outputs. The XLR pro level analog outputs are useful to me since my Crown power amps have XLR inputs for my subwoofers (and buttkicker) channels. With a XLR to RCA adapter I can take the preouts from my Yamaha AVR for the "HT Bypass" mode.

4. SMSL M8 DAC's. With the nanoDIGI solution, it is very easy to select (and later upgrade) the DAC's that are driving the tweeter and woofer power amplifiers. Also in my previous PLLXO (passive) solution, I had to include the input/output impedance of my preamp and poweramps in the PLLXO component value selections. Now with this active solution I can use whatever amps and DACS I wish. The SMSL M8 uses the ESS9018 DACs which measure and review well.

5. HT Bypass vs Music Mode. My system is for both 2 channel and 7.2 ATMOS hometheater listening/viewing. I need to be able to switch with a Harmony remote between the modes. Unfortunately the Focusrite USB interface does not support IR commands. Also, the Windows Control panel software for Focusrite does not support command line options. I did try using some Windows macro recording software (autohotkey) to trigger changing modes of sending IN/OUT routing thru the Focusrite to implement different audio routing modes. I could never get the macros to trigger reliably. So I added an existing legacy Firestone Audio Bravo to my setup.

HT Bypass Mode:

Yamaha AVR L/R Preout -> Focusrite XLR/RCA adapter input -> Focusrite SPDIF 24/96K output -> nanoDIGI SPDIF input -> nanoDIGI SPDIF out -> Focusrite (to subs) and SMSL DACS -> Parasound HCA-1000 power amps -> Magnepan Twt/Woofer panels.

The SVS, HSU and Buttkicker bass frequencies follow a similar initial path and then to the Focusrite analog outputs.

Music Mode:

Windows 10/Jriver PC -> Firestone Audio Bravo USB to TOSLINK 24/96 output -> nanoDIGI TOSLINK input -> nanoDIGI SPDIF out -> Focusrite (to subs) and SMSL DACS -> Parasound HCA-1000 power amps -> Magnepan Twt/Woofer panels.

The SVS and HSU bass frequencies follow a similar initial path and then to the Focusrite analog outputs.

I recognize that I am using the TOSLINK input to the nanoDIGI for my "audiophile" music mode and the potentially higher quality SPDIF coax for the HT Bypass mode. However the Focusrite device only has SPDIF output.

In a following post I will describe the improvement in sound.

 

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RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 17, 2019 at 16:15:48
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 Reserved for Listening impressions.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 18, 2019 at 10:02:44
Satie
Audiophile

Posts: 5430
Joined: July 6, 2002
 I like how you have the option to do EQ with modern filters before entering the nanoDSP. You also solved a long run issue with DSP crossovers - low performing DAC and analog sections with the digital In/Out for the nanoDSP crossover.

The downside here is the really large box count for the implementation.And each item needs to be set. In this situation, perhaps the better idea is to get a prior generation high end pre/proc from Theta Proceed etc.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 18, 2019 at 10:50:36
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 yes it is a large box count. But that is because I am supporting both 2 channel and HT listening plus 4 subwoofers in a single setup. The minidsp SHD solution would integrate the functions of the AudioPC, Bravo, Focusrite and DACs dramatically reducing the box count. But it does not have the ability to support 8 channels out for my subs.

Your point is well taken tho, lots of boxes, lots of interface cables and opportunities for issues on power up power down order.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 21, 2019 at 18:43:19
johnvb
Audiophile

Posts: 496
Joined: October 26, 2011
 I also (still) use a NanoDIGI, but now only as an EQ between a streamer and DAC, before the preamp. I do have one of those iFi SPDIF purifiers added to the input of the DAC, to help with any jitters.

Are you concerned with loss of bits using the Nano after the preamp? Not audible? Or are you using the Nano for volume control? I used a multichannel analog preamp after the Nano, when using it like you are.

Noticed you have SMSL dacs, I just upgraded to the economical SMSL Su-8 model, wow what a great sounding DAC, best I've had in my system.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 22, 2019 at 06:50:52
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 For music listening, my volume control is done in the digital domain with jriver mediacenter software. I do not use the nanodigi for volume control. The nanodigi input/output levels I believe are set to -1 db for a little safety margin for clipping. The one exception is the nanodigi channels feeding the HSU subwoofers. Because I am implementing the HSU bass optimizer filter in the nanodigi, I needed to account for the 6.5db gain of the filter and possible clipping when listening at max volume. I have a -10 db level set on the output of that channel in the nanodigi. I then increased the level control in the Crown power amp for the HSU's to level match my SVS and HSU subs at my listening position.

To reduce the issue of loss of bits, I have the analog level controls on my Parasound HCA-1000A power amps set down a bit, such that with the jriver volume control is near 90% at my max volume listening level. Such that the loss of bits for reducing volume is minimized.

When in Hometheater listening mode, I use the Yamaha AVR for volume control. I have the Yamaha front left/right preout gain settings bumped up a bit so that the approximate signal gain when going thru music or HT mode is the same. So that I don't blast myself when switching modes with my remote between the two volume schemes.

In summary, the important thing to do is to set max volume prior to the level of clipping in your entire audio chain from source leading upto your power amps. Assuming you have gain controls on your power amps use those to reduce the volume to whatever your max volume listening level is. That way the attenuation require in the digital domain is reduced just to fine tune volume level for whatever you are listening too.

There is an interesting posting here that talks about the issue of loss of bits. Basically try and keep your digital volume attenuation to less then 20db with a 24bit resolution DSP and DAC system.

http://archimago.blogspot.com/2019/02/musings-why-bother-with-24-bit-dacs.html

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on March 22, 2019 at 06:59:59
johnvb
Audiophile

Posts: 496
Joined: October 26, 2011
 Good deal, thanks for the link.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 09:11:46
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 I just thought I might update this thread. After living with the nanodigi based active crossover for some time I am still very happy with the results. I have since started experimenting with different power amplifiers. Given the nanodigi active crossover, I can use different amps on the tweeter vs woofer circuit.

I started with the Parasound HCA1000a power amps on both tweeter and woofer circuits shown in the head of this thread. But I am now using a Nelson Pass Class A Aleph 3 clone on the tweeter and a Panasonic XR57 Class D amp on the woofer.

The Class A amp on the tweeter adds a tremendous amount of air and live feeling to the upper frequencies. The Class A amp is rated 30w/8ohms and 60w/4ohms. So it is lower power, but for the tweeter circuit you need much less power overall.

I will say that the Class A amp in general measures like crap. But if you read Nelson Pass's whitepapers on distortion vs the simplified no feedback designs you can see that there are many benefits to his approach to amplification.

My measurements of my Clone Amp:
https://www.audiosciencereview.com/forum/index.php?threads/class-a-aleph-3-clone-measurement.10646/

Pass whitepaper on Class A amps:
http://www.firstwatt.com/pdf/art_dist_fdbk.pdf


The Class D XR57 is taking the SPDIF digital directly out of the nanodigi and there is no extra DAC in the path. The XR57 was discussed as a giant killer amp years ago and I had one in storage. For two channel only it has an automatic "dual amp" feature which allows the XR57 to drive the left and right woofer with a total of 4 amp channels increasing the current/wattage produced. The Class D amp is great for the woofer circuit adding what sounds like an extraordinary amount of control to the woofer bass frequencies.

Measurements on my XR57:
https://www.audiosciencereview.com/forum/index.php?threads/panasonic-sa-xr57-multi-channel-receiver-review.10480/
https://www.audiosciencereview.com/forum/index.php?threads/critique-my-measurement-setup-panasonic-xr57-avr-example.10589/

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 10:46:30
BDP24
Audiophile

Posts: 1070
Location: Vancouver, Washington
Joined: September 12, 2013
 My head hurts. ;-)

 

Tweeter Protection Capacitor, posted on January 3, 2020 at 11:03:39
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011








One unfortunate development from the Chinese clone Class A were power on and power off thumps. I added a 68uf capacitor inline on the positive speaker cable going from the amp to the tweeter section of my speakers. With an active crossover setup like mine, there is no passive crossover components between the amp and the speakers. So any unplanned energy from the amp goes directly to the tweeter.

The goal here was to add a capacitor with a filter point at least 2 octaves below the active filter point with the intent that the additional cap would not impact the response of the tweeter circuit but would prevent DC and low frequencies from making their way to the tweeter panel. The theory is also that that cap 2 octaves below would not impact the sound in the more critical frequencies of the Magnepan 1.6 tweeter panel. I used an erse audio Pulse-X cap for this exercise. Not super high end but not bargain basement either.

Once I put the cap in the circuit, I was able to measure the speaker response with REW EQ software. I did measure a slight 1 db reduction in the 200-500hz region of the speaker response. So I used the nanodigi PEQ function to boost those frequencies to compensate.

The thumps are gone now. A great set of posts about the idea behind the cap protection circuit is here:
https://www.audiofrog.com/community/tech-tips/to-cap-or-not-to-cap-tweeters-in-systems-with-active-crossovers/

 

REW Measurements: 4 subs blended, posted on January 3, 2020 at 11:06:33
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011






I did measure with REW EQ software the results of blending my 2 SVS SB1000 subs and 2 HSU TN1220 at my listening position. I was able to achieve a very even response and the multiple subs evened out the freq and waterfall response graphs nicely. Graphs shown are all 4 subs plus Left and Right Magnepan 1.6's from my listening postion.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 11:31:45
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 ah but your ears would be in heaven.

all kidding aside, as an electrical engineer by training part of me likes the complexity. but my wife does not. That is why all of the complex connections and tweaking are in an equipment closet adjacent from the listening room. In the listening room is an android tablet plus harmony remote that automates all the turn on /off and AV/music selection tasks for my family.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 13:06:02
josh358
Industry Professional

Posts: 12376
Joined: February 9, 2010
 Have you considered doing everything in JRiver and sending everything through an OKTO DAC? Much simpler signal flow, to say the least . ..

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 13:08:56
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 Jriver running the crossover functions on a PC adds too much latency to my front speakers making them not integrate well with the rest of the ATMOS speakers hosted on the AVR setup when watching movies.

also, I have switched out the PC/Jriver for a raspberry pi running volumio for music since originally posted on this thread.

 

RE: My DIY Story: nanoDIGI DSP based active crossover and 4 subwoofer integration, posted on January 3, 2020 at 13:35:46
josh358
Industry Professional

Posts: 12376
Joined: February 9, 2010
 Makes sense. I wish everything (including video players) had the option of adding delay . . .

 

RE: I changed from 10x10HD to nanoDIGI last year ..., posted on March 28, 2021 at 23:59:09
andyr
Manufacturer

Posts: 12655
Location: Melbourne
Joined: September 2, 2000
 It substantially improved my sound (due to the ADC I now use for my phono stage - to input into the nanoDIGI - and the 4x Topping E30s that handle the 8x output channels).

So my signal chain is:
* phono stage --> ADC (kit from Uwe Beis, running at 96kHz)
* ADC output plus 3x digital devices (CDP, DAB+ tuner and TV box) --> 4-way digital source selector
* digital output from the source selector --> nanoDIGI 2x8
* nanoDIGI --> 4x Topping E30s
* Topping E30s --> various power amps driving:
- a sub
- bass panel
- mid panel
- 3 ohm true ribbon, on each channel.

I don't use a series cap on the ribbons as the amps driving them does not produce a thump, on turn on/turn off.

Andy



 

RE: different Amps, Different DACs, alignment issues?, posted on March 28, 2023 at 11:38:18
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011






I am back at tweaking my active DSP based crossover setup. I am presently using a Pass Aelph 3 clone Class A amplifier on the tweeters and a old Panasonic XR-57 Power DAC Digital Amplifier on the woofers. This replaces the two Parasound HCA-1000 discussed in the original thread here.

The sound is really very good with the Class A amp on the tweeters and the Class D amp on the woofers. However I was concerned that the different paths and amps would introduce a significant difference in delay/latency and cause timing alignment issues between the tweeter and woofer panels.

With REW I measured. Ignore the differences below 60hz since the two measurement setups with sub cut off frequencies are different in that region.

If you look at the OEM crossover measurement (first graph) you can see that the woofer and tweeter regions appeared pretty aligned. However with the Nanodigi setup (second graph) with the different DAC's and Amplifier paths the two drivers are off by about 30msecs. The nanodigi allows me to add delay but maxes out at 9msecs which is not enough to compensate for the 30msec latency differences.

What are peoples thoughts on the alignment issues and what sound listening issues I may be introducing to myself with this experiment? The Panasonic XR57 is an AVR with several distance and speaker size settings. I have gone in and turned all of that off for this experiment.

 

RE: different Amps, Different DACs, alignment issues?, posted on March 30, 2023 at 12:44:53
Davey
 The nanoDIGI itself only has an inherent delay of about 1 millisecond.
So, any big relative delays are coming from some other component(s).

Dave.

 

RE: different Amps, Different DACs, alignment issues?, posted on March 30, 2023 at 17:07:56
dumpingground
Audiophile

Posts: 264
Joined: February 23, 2011
 the relative delay difference is definitely coming from buffering/processing/latency induced from the Panasonic XR57 AVR on the woofer panels vs the relatively low latency Class A power amplifier on the tweeters.

 

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