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Article: Digital Signal Processing - The Ultimate Guide To High End Immersive Audio


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8 hours ago, Keith_W said:

Yes Mitch I know that Acourate is not for everybody. I know someone who is putting together a 5.2 system and asked me to help him correct his system with DSP. He wanted to use Acourate. I strongly advised against it, my recommendation was Audiolense + send you an email.

 

I go through that time alignment procedure for my 8 channel system (2x active 3 way speakers + 2 subwoofers) and it takes me hours to do it. So I was pretty impressed when a friend who used Audiolense came over with his laptop. 30 minutes was spent explaining my system architecture to him, downloading drivers, performing channel checks, and all the usual futzing around before a single sweep can be done. But when he actually got to it, the whole thing was done within 15 minutes, from crossover generation to usable filters and verification measurement (had to be done in REW, because Audiolense can't do verification measurements?). I was amazed when I saw the step response, it was textbook perfect. Not that I can't get the same result, but despite my proficiency, it takes me a long time. 

 

Many years ago, DSP correction via Acourate/Audiolense was much less well known and it was difficult to get help. This was even before your book came out. I posted a question asking about it in another forum, and a very kind member rang me from the USA to talk me through it. I have never forgotten his help and I am grateful for as long as I remain in this hobby, which will stay with me as long as I have intact hearing! I hope to do everything I can to help people see the benefits of DSP, in the same way that he helped me.

 

I am not partial to one software solution over another, I think there are different advantages and disadvantages to different software packages that might suit some folk more than others. Acourate has a very "Teutonic" approach which is both good and bad depending if you are the kind of person who enjoys doing your own car maintenance.

 

When I first bought your book I thought that I am way out of my depth here, but after 8 years and multiple re-readings, I have gone on to look up all the references you cited and come to my own conclusions. For example, you recommend measuring without the sofa. I asked myself why I should do that, when the listening sofa is always at that position? So I performed the experiment - measure with and without sofa, correction with/without sofa, and verification measurement with/without sofa. There is a noticeable difference measurably and audibly. Conclusion: measuring and correcting without sofa and then performing the verification measurement with the sofa in situ messes up the correction, but it actually sounds better. 

 

Another example: Toole says that the Harman target is not a target, it is the result of putting a speaker that measures flat under anechoic conditions in a room, this will naturally roll off the higher frequencies. In your book you suggested choosing a target to preference. So I tried Toole's suggestion, I knew that limitations of measurement means that any freqs < 425Hz (transition zone in my room calculated from 4x Schroder) would be meaningless, but that is OK because I was planning to use a different bass correction strategy anyway. I corrected the nearfield response to flat, then applied correction < Schroder. To my surprise, verification measurements showed a rising treble response at MLP instead of a falling one! Anyway, after a lot of investigation it turns out that the directivity of the horns was causing them to behave differently to the more omni woofer. So what does that say about Toole? I think it may not apply to horns, although I am not brave enough to say that to him ;) My system, I do what I want, and I use my own target curve, as per your recommendation in your book. 

 

Anyway, to other readers of AS: DSP is a really worthwhile pursuit. I think that in 2024, every system should have DSP. I would go further than Chris and say that anybody who refuses to consider it is stuck in outdated thinking and misplaced priorities. 


What an enjoyable read @Keith_W. Its about the journey and destination. 
 

When I started going down the DSP road I assumed there was a single objective destination that math and physics would lead me to. I quickly learned, with tons of information from Mitch, that the objective hands off to the subjective once the fundamentals are taken care of. Target curves and final adjustments are all about preferences. Once I grasped that, I had much more fun working with Mitch to get the best sound possible. 
 

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Thank you for a very informative article. It is very interesting to see immersive playback unfold and you are spearheading that front to a large extent. However, don't forget about the antiquated 2-channel setup entirely :) and we can use some network DSP there as well. Had to smile that you did draw the immersive audio line by subtracting the use of a screen.

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8 minutes ago, SQFIRST said:

Thank you for a very informative article. It is very interesting to see immersive playback unfold and you are spearheading that front to a large extent. However, don't forget about the antiquated 2-channel setup entirely :) and we can use some network DSP there as well. Had to smile that you did draw the immersive audio line by subtracting the use of a screen.

Thanks for the kind words. 

 

I will never forget about two channel. I listened to a great two channel album this morning on my main system and I listen to two channel at my desk all the time. Immersive is just another option for people. 

 

Network DSP for all, would be great. We need to get HiFi manufacturers to embrace Ravenna. It puts everything on the network and opens up a world of possibilities. If it's good enough to capture a live orchestra, where there are no second chances, it's good enough for HiFi. 

 

No screens allowed in my room :~)

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4 minutes ago, The Computer Audiophile said:

Network DSP for all, would be great. We need to get HiFi manufacturers to embrace Ravenna. It puts everything on the network and opens up a world of possibilities. If it's good enough to capture a live orchestra, where there are no second chances, it's good enough for HiFi. 

 

I use Ravenna. I am sold on its benefits. For me, the main benefit is that I do not need to look for a 16 channel DAC. There are very few of those around! Instead, I can buy two 8 channel Ravenna DAC's and a microphone interface. Ravenna ties all the equipment together and tells the PC "I am a device with 16 DAC channels, 4 microphone inputs, and 8 digital inputs" (or something like that). You can put together as many channels as you want. 

 

The problem with Ravenna (and also Dante and AVB) is that they are pro audio standards. Not easy for us amateur hobbyists to set up. I already find my RME intimidatingly difficult, let alone Ravenna which adds the complexity of network audio and multiple modes into the mix. I keep telling myself that I am a home audio enthusiast. I am not running a broadcast studio, or routing audio in a stadium, or an airport, or any situation where network audio would be a massive advantage. But now that I am starting to run out of DAC channels, I appreciate the flexibility of Ravenna. Someone who is into immersive audio with more speakers than me would see more of a benefit. 

BTW, aren't you the guy who blew up his speakers when trying out the Merging Anubis? ;) Not easy to set up, are they. 

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5 minutes ago, Keith_W said:

BTW, aren't you the guy who blew up his speakers when trying out the Merging Anubis? ;) Not easy to set up, are they.

Ha! yes, I blew a pair of Wilson Audio TuneTots up with an Anubis. I've come a long way. Now I can configure it with my eyes closed and I know the Anubis and HAPI Mk2 inside and out. Right now I have the Anubis setup to receive 7.1.4 from my MacBook Pro, and 4.0, 5.1, and 7.1.4 from an Aurender ACS10. I just switch "inputs" on the Anubis screen at my listening position. It's so flexible. I love it. 

 

This complexity is only there for people like us who want to know everything about the components and how to configure them. Normal people (we aren't normal), could have it configured by an expert, then never touch it. 

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7 hours ago, The Computer Audiophile said:

Target curves and final adjustments are all about preferences. 

 

Welllllllllllllllllll that is a bit of a can of worms. If you read what Toole says in his book, he says that good speakers should have two properties: (1) they measure flat under anechoic conditions, (2) they have constant directivity. If you place such a speaker in a room and listen farfield, you will obtain a Harman-like curve (there is a good video by Erin on Youtube that explains why). Toole has said himself on another forum that equalizing a speaker to reproduce the Harman curve at MLP is wrong, because an on-axis correction also affects the off-axis response, which will produce reflections which are spectrally incorrect. There is no "choose your target curve based on your preference". 

 

Toole's motivation is to narrow the "circle of confusion" - have the studios produce music mastered through standardized sound systems, played back in our homes using speakers designed to achieve certain standards of performance. The recordings have to be mastered on systems so that they are faithful to the original sound, and have to be played back on systems that reproduce the sound of the master faithfully and accurately. Only then can we have "accurate sound". 

 

However, in the real world, even studios can not get something as basic as the frequency response correct. Genelec did a study using their GLM tool, which is a calibration tool for their speakers. They observed a wide variety of frequency responses in studios. And this is only for studios with Genelec speakers, who bothered to pay extra for the GLM tool. In reality the variance is probably much worse than that Genelec study. 

 

I would argue that this gives me license to adjust the frequency tilt as I please. For each recording, if necessary. So, like you, I have gone for a preference target. I am not an authority figure, I am merely an amateur hobbyist in an ocean of amateur hobbyists. I have no business arguing with Toole. Or Mitch, for that matter. BUT ... sometimes authority figures disagree, leaving us minnows confused. So I read what they say, try to understand their points of view, and make up my own mind. After all, the sign of an educated person is the ability to entertain contradictory points of view and weigh them up fairly. 

 

BTW I recently came across a new method for generating a target curve that removes the "room transfer function", restoring your speaker to a flat anechoic response. You perform a nearfield MMM of your speakers, then perform a MLP MMM. The idea is that the MLP MMM captures the "speaker + room" response, and the nearfield is speaker only. If you subtract the nearfield MMM from the MLP MMM, you will obtain the "room transfer function". If you set this as your target curve, it will correct the nearfield response to flat. I have tried this, and it works for frequencies above transition (i.e. 4x Schroder, about 440Hz in my room). If you want to learn more, google "Magic Beans room correction joe n tell". You will find some videos. 

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I have a Denon AVR, although this is more used as a processor as I have external amps for all but the height speakers.

 

This comes with Audyssey as the default "built in" software. Optional software is also available, Dirac Live (limited Bandwidth), Dirac Live (Full Bandwidth) and Dirac Live Bass Control.

 

I am assuming that Dirac Live Bass Control is of no use to me, I do not use a subwoofer.

 

So I am thinking of getting the licence for for the Full bandwidth Dirac Live Room Correction. The licence is $349.

 

I presume that the Full Bandwidth Dirac option is superior to Audyssey?

Windows 11 PC, Roon, HQPlayer, Focus Fidelity convolutions, iFi Zen Stream, Paul Hynes SR4, Mutec REF10, Mutec MC3+USB, Devialet 1000Pro, KEF Blade.  Plus Pro-Ject Signature 12 TT for playing my 'legacy' vinyl collection. Desktop system; RME ADI-2 DAC fs, Meze Empyrean headphones.

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2 hours ago, Confused said:

I have a Denon AVR, although this is more used as a processor as I have external amps for all but the height speakers.

 

This comes with Audyssey as the default "built in" software. Optional software is also available, Dirac Live (limited Bandwidth), Dirac Live (Full Bandwidth) and Dirac Live Bass Control.

 

I am assuming that Dirac Live Bass Control is of no use to me, I do not use a subwoofer.

 

So I am thinking of getting the licence for for the Full bandwidth Dirac Live Room Correction. The licence is $349.

 

I presume that the Full Bandwidth Dirac option is superior to Audyssey?


I have no direct experience with Audyssey, but I know many people who believe your assumption is correct. 

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Audyssey is ok, particularly if your Denon will allow use of the professional measurement kit, as my Marantz AV-8802A can do. But, I agree with @The Computer Audiophile: Dirac is said to do substantially better, certainly than the standard Multeq XT32 Audyssey that your Denon likely has built in. And I’ve moved to Audiolense XO, which in my personal experience is way better than Audyssey. You might consider that as an investment over the Dirac license. JCR 

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One of hybrid approaches could be use of Genelec SAM speakers with GLM software.

It allows for speaker-level bass management with optional 9301B interface (~$1k).
Linear phase from 100Hz up or low latency (~3ms); your choice.

Not as good spec as computer based DSP, but pretty good (and expensive).

You only need Merging Horus or Hapi (depending on number channels) without and DAC cards. DACs are built in to speakers.

If that is not enough, you can optionally use computer based DSP before sending stream to Merging.

 

Cheers,

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19 hours ago, maxijazz said:

One of hybrid approaches could be use of Genelec SAM speakers with GLM software.

It allows for speaker-level bass management with optional 9301B interface (~$1k).
Linear phase from 100Hz up or low latency (~3ms); your choice.

Not as good spec as computer based DSP, but pretty good (and expensive).

You only need Merging Horus or Hapi (depending on number channels) without and DAC cards. DACs are built in to speakers.

If that is not enough, you can optionally use computer based DSP before sending stream to Merging.

 

Cheers,

 

Hi @maxijazz Thanks for bringing up this option. It raises some questions I've been thinking about over the weekend. 

 

If using Genelec speakers with built-in DACs and DSP, where does the volume control take place and how does the user control it? For example, if I'm streaming from JRiver to a HAPI to Genelec speakers. Without an Anubis, the user would have to be physically turning the knob of the HAPI for volume control. 

 

Also, if volume control is done prior to DSP inside the speakers, is this a big no-no? In my head this is an issue, but I honesty don't know if it plays out this way. 

 

I've been thinking of putting a DSP box between my Anubis and HAPI, but my hesitation is that the Anubis does volume control and this will reduce resolution for the DSP filters. 

 

@DigiPete do you have experience with Genelec DSP?

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35 minutes ago, The Computer Audiophile said:

 

Hi @maxijazz Thanks for bringing up this option. It raises some questions I've been thinking about over the weekend. 

 

If using Genelec speakers with built-in DACs and DSP, where does the volume control take place and how does the user control it? For example, if I'm streaming from JRiver to a HAPI to Genelec speakers. Without an Anubis, the user would have to be physically turning the knob of the HAPI for volume control. 

 

Also, if volume control is done prior to DSP inside the speakers, is this a big no-no? In my head this is an issue, but I honesty don't know if it plays out this way. 

 

I've been thinking of putting a DSP box between my Anubis and HAPI, but my hesitation is that the Anubis does volume control and this will reduce resolution for the DSP filters. 

 

 

In example, in 8351B_operating_manual_rev_b.pdf, on page 7, there is Figure 12.
It is best option to use Genelec SAM speakers with GLM4 software through GLM kit.
You can get optional volume controller 9301b, that you connect to the GLM kit. It will apply your volume level at "Level  and optional gain" place on Figure 12. 
I have the GLM kit powered by USB2 in my music server (=> whenever i start music server, the GLM kit gets powered at same time).

There is also optional 9101B remote, but it requires GLM4 software be up and running on a computer (if i remember well).
You can control volume directly from GLM4 software using mouse (on-screen slider), but it requires computer and software up and running (which i have headless).

 

Without the GLM4 software or 9301b volume controller (or newly released 9320A, which is expensive stuff), you must use an analog or digital volume controller somewhere before signal reaches speaker (your Anubis would do).

 

 

 

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I ran new sweeps last week using a cross-spectrum calibrated EMM-6 and a Teac UH-7000 directly driving my amplifier.  Forgot to turn system sounds off and thankfully the Revels are robust. 😬 I couldn't get the mic align to work in LSR3 on my laptop so I eyballed it and used LSR2 and after a few iterations apparently hit the gold spot.  Although I bought Mitch's book almost 7 years ago, I just finished it in September.  So, this was my first go at it post-book reading.  I built double-length 130k tap filters and wound up with almost perfect IACC numbers for the first time ever; the step response was an almost perfect triangle and the channels tracked remarkably well with no changes to the default windowing or pre-ring compensation.  There's no question that acourate is an amazing DSP toolkit.  I will probably try Audiolense next just because.  I am waiting for the next edition of your book that includes a full treatment of Audiolense and anything new for acourate users too. I couldn't imagine my system without DSP and have been using acourate for more than 10 years now and also Dirac as well for multichannel.  I wish to compare my theater/multichannel set up with Audiolense filters vs. Dirac +DLBC and DART as I can drive my HT preamp from HQPlayer through HDMI from Roon.  What a time to be an audiophile!

 

image.thumb.jpeg.a4a84e289e35c7e49a6d3042fc9b2a99.jpeg

 

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On 1/28/2024 at 7:26 PM, jrobbins50 said:

Audyssey is ok, particularly if your Denon will allow use of the professional measurement kit, as my Marantz AV-8802A can do. But, I agree with @The Computer Audiophile: Dirac is said to do substantially better, certainly than the standard Multeq XT32 Audyssey that your Denon likely has built in. And I’ve moved to Audiolense XO, which in my personal experience is way better than Audyssey. You might consider that as an investment over the Dirac license. JCR 

 

It looks like you are correct. From the Denon specifications:

 

image.png.a29ae7e8f71ca7e67044309cda51ad17.png

 

One point to clarify, I am already using convolution filters created using Focus Fidelity Filter Designer for my 2 channel system. This is streaming via PC / HQPlayer / NAA. I am very happy with both the functionality and the ultimate sound quality results from FFFD.

 

So I am only thinking of Dirac for the 7.4 ATMOS side of things. Am I right that Audiolense is for PC only? For my surround system the source will be Blu-ray discs, Apple TV and similar, nothing streamed from a PC. So this takes me back to Dirac being my best option I think, for multi-channel at least.

Windows 11 PC, Roon, HQPlayer, Focus Fidelity convolutions, iFi Zen Stream, Paul Hynes SR4, Mutec REF10, Mutec MC3+USB, Devialet 1000Pro, KEF Blade.  Plus Pro-Ject Signature 12 TT for playing my 'legacy' vinyl collection. Desktop system; RME ADI-2 DAC fs, Meze Empyrean headphones.

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1 hour ago, Confused said:

So I am only thinking of Dirac for the 7.4 ATMOS side of things. Am I right that Audiolense is for PC only? For my surround system the source will be Blu-ray discs, Apple TV and similar, nothing streamed from a PC. So this takes me back to Dirac being my best option I think, for multi-channel at least.

 

One of the really cool benefits of using a protocol like Ravenna / AES67 is that you can route audio from non-computer devices to a computer for DSP. For example, I could use a Blu-ray player or Apple TV connected to an Arvus H-1D (HDMI in / AES67 out) and send that audio stream to Hang Loose Convolver for room correction, then out to my audio system. One can also just rip the Blu-ray and stream from Apple Music to get the same content if desired. 

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5 hours ago, Confused said:

So I am only thinking of Dirac for the 7.4 ATMOS side of things. Am I right that Audiolense is for PC only? For my surround system the source will be Blu-ray discs, Apple TV and similar, nothing streamed from a PC. So this takes me back to Dirac being my best option I think, for multi-channel at least.

I think for your case, Dirac is the way to go. Plus, Dirac allows for correcting multiple subwoofers with a Dirac Live Bass Control license and soon will also support Active Room Treatment too.  These are good features that distinguish Dirac from other embedded RC solutions and may actually e a better way to go than building filters in Audiolense, particularly for Apple Music streaming. While I will have the ability to compare Dirac to Audiolense, I suspect that I may actually prefer Dirac because of the bass control and eventually active room treatment even if Dirac is not as accurate as Audilense in phase correction and time alignment.  Different rooms and speakers benefit from different corrections, so I think which of them is best is going to vary quite a bit.

 

image.thumb.jpeg.a4a84e289e35c7e49a6d3042fc9b2a99.jpeg

 

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