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


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On 1/26/2024 at 9:06 PM, Keith_W said:

 

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. 

What is then your opinion about such a statement by dr Floyd Toole in ASR about Magic beans ?

"If a loudspeaker is well designed, i.e. free from audible resonances, spectrally flat on axis, and smooth off axis, the only adjustments that should be necessary at middle and high frequencies are broadband “tone control” spectral balance tweaking to address variations in program material. Low frequency room mode problems have to be addressed as a separate problem (see Todd Welti papers or my book), and once solved, again only “tone control” adjustments will be necessary for program variations. No fixed “calibration” can be perfect for all program material.

People keep looking for money-making ways to sell “calibrations” and most of them are lacking in some way. This is another one. It has a chance of making a truly bad loudspeaker sound better, but, in my opinion, it has an equal chance of degrading a truly good one. And so it goes . . . Pick the right demo material and the customer will be thrilled."
 

https://www.audiosciencereview.com/forum/index.php?threads/mmm-approach-and-a-new-calibration-app-magic-beans.50297/

 

I certainly concur on using DSP, including Virtual Bass Array, to address Low frequency room mode problems (no correction above 464 Hz afaic but 2 octaves wide "tone control") that I address by using different in room corrections to adjust to program material that can be best suited by huge bass boosts following JBL Synthesis or Harman Target Curve or by absolutely flat response.  Absolutely flat certainly works on recent material such as Yuchan Lim's Liszt and may be backed by Sonarworks or Genelec's recommendation : "To accurately monitor what is recorded on the hard drive or tape machine, the monitoring system also has a flat response at the listening position." (https://support.genelec.com/hc/en-us/articles/360013436179-What-should-be-the-target-response-of-a-monitoring-system-at-the-listening-position ). It makes sense from mastering perspective : if the final customer has (typical) room gain (bass over flat) and distance air absorption causing HF rolloff, it will sound with a (generally) flattering downward tilt. However, even with modern mastering I rather use the attached target that I get with strictly no correction above 464 Hz since, from psychoacoustic perspective, respecting a bit of natural room gain and air absorption matters too. This might explain the reluctance of engineers to monitor in unnatural conditions with a strictly flat response. At home,  I find it helps letting your acoustic being replaced by the acoustic of the recording venue (because the latter is larger : see I read Floyd Toole's book too 😀).

 

But I'd be happy to read more about your findings on Magic beans

putative Genelec.jpg

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If you look further in that ASR thread you linked, you will see my experiments with Magic Beans. I do not agree with Toole's opinion, because I don't think he understood the objective of Magic Beans. Toole is famously against custom target curves that replicate the Harman curve. In that same thread he said it is not a Harman "target", it is a Harman "result", i.e. what the speaker naturally reproduces at the MLP if the speaker was designed to be flat under anechoic conditions. The idea of Magic Beans is to restore the anechoic performance of the speaker by removing the "room transfer function". It is not about artificially creating a Harman target. And even if it was, I have no objection to it, provided that speaker directivity is constant and it does not mess up the off-axis response. 

 

Toole also thinks that this is some kind of money making gimmick. This is not true, anybody who has DSP software which has the ability to manipulate curves is able to copy the workflow and implement Magic Beans correction for free. I posted an Acourate workflow in the same thread. That experiment did not cost me a cent. 

 

In any case, I have said upthread that I have no business arguing with Toole. I personally think he is incorrect on this point, but you should remember that my opinion carries no weight. I am an amateur hobbyist. He is Toole. Having said that, I am under no obligation to do everything he says with my own system. 

 

Unfortunately, my speakers are not a candidate for Magic Beans correction. This is because they have mixed driver types, with horns >500Hz and normal woofers/subs below. I have measurements that demonstrate that the output from the horns does not decrease in volume with distance, whereas the woofers/subs decrease as expected. This produces an upward tilting curve at MLP, which is the opposite of what nearly every other speaker type produces. The Magic Beans correction actually does correct the nearfield response to flat (indicating that I followed the procedure correctly), but it produces an upward tilting response at MLP. After I gave my feedback to joentell, he implemented a "directivity detect" feature in his app. 

 

There is a detailed analysis of my speakers on ASR under my system thread. It does not behave like a normal speaker, which is why the DSP solution is different to a normal speaker. 

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4 hours ago, Keith_W said:

If you look further in that ASR thread you linked, you will see my experiments with Magic Beans. I do not agree with Toole's opinion, because I don't think he understood the objective of Magic Beans. Toole is famously against custom target curves that replicate the Harman curve. In that same thread he said it is not a Harman "target", it is a Harman "result", i.e. what the speaker naturally reproduces at the MLP if the speaker was designed to be flat under anechoic conditions. The idea of Magic Beans is to restore the anechoic performance of the speaker by removing the "room transfer function". It is not about artificially creating a Harman target. And even if it was, I have no objection to it, provided that speaker directivity is constant and it does not mess up the off-axis response. 

 

4 hours ago, Keith_W said:

After I gave my feedback to joentell, he implemented a "directivity detect" feature in his app. 

 

Above Schroeder, at most above a transition zone that should not extend beyond 500 Hz, the speaker rules. And if it's well conceived, most notably regarding directivity, it behaves so that it measures "Harman" or Toole's ideal steady state, at least above 500 (we all have to take care of LF one way or the other I guess). If not, one should consider changing his/her speakers, not DSPing (but for broad tone controls) ; that's the essence of Floyd Toole's research findings. Personally I always stick to brands that have at least one foot in HQ production, be it HQ broadcasting or recording (I'd check JBL/Revel, B&W, Genelec, Cabasse...) even if they don't have the most powerful marketing clout. "After I gave my feedback to joentell, he implemented a "directivity detect" feature in his app." Gee.....!!! Oh I think Floyd Toole dug perfectly, except maybe for money if Magic Beans is non profit

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I should point out that Toole thinks that we should correct below Schroder. Above Schroder, he says it is OK to apply broad tone controls, but he thinks that applying correction to a target is the wrong approach. He is essentially arguing against more granular correction - after all, a "broad tone control" is the same as a very loosely applied target curve. When you make your correction, it is trivial to select how granular you want your correction to be. You can make it really hug the target curve, or you could make it sort of "trend" towards the target curve (the Toole approved approach), or anything in between. The granularity of the correction is a continuous variable. Since it is so easy to do, you can make a range of filters and listen to which one you think sounds best.

 

I don't have a firm opinion on this one, I do both. I can flip between the filters with ease, a push on the button on my convolver and I have a new filter loaded. And if you use HLC, the music doesn't even stop. 

 

Of course, making the on-axis response look perfect might mess up the off-axis response. So I regularly check what is going on off-axis as well. Same procedure, 45 deg off axis, and your choice of SPS or MMM. 

 

And BTW, I wouldn't dismiss the Magic Beans idea. Do you understand how it works? Those videos don't do a very good job explaining it, you really have to watch a few videos and aggregate all the information together to understand what the intention is. I posted a summary of my findings in that ASR thread, and joentell thought that it was an accurate description of the method. 

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1 hour ago, mitchco said:

@kalpesh

 

As I said back in 2018 at ASR, I am in total agreement. The fundamental issue is there are not too many well designed speakers. Certainly not compared to the "ideal" speaker.

 

Using modern DSP/DRC with frequency dependent windowing, we can let low frequency room reflections into the measurement microphone and with DSP smooth out those room modes and non-minimum phase response. As we transition form room modes (i.e. waves) to rays we let less of the room reflections into the mic so we are only correcting the direct sound of the speaker and not the room reflections.  In other words, above 800 Hz or so we are only using DSP/DRC as a tone control. 

 

Really, I have just visited your site and the exemples here : https://accuratesound.ca/digital-room-correction-drc-calibration/ don't look at all like tone controls above 800 Hz but minute details corrections. Think of Audio Palette, controls span over 2 octaves 

 

1 hour ago, mitchco said:

 

 

As far as the downward tilted response, Floyd explained here. I spent 10 years as a pro recording/mixing engineer in a variety of studios with many calibrated monitors, none of which had a flat response at the listening position. Unless one was deaf, it is way too bright sounding. For sure, some DRC s/w does indeed eq for flat, but it is not SOTA. As Sean Olive has pointed out in his presentation on The Subjective and Objective Evaluation of Room Correction Products. See slides 22, 23, and 24 to see why flat in-room response is not the preferred target. Yah, "target."   

but play a track recorded and mastered with flat response at LP and it will sound fine. It's always solving the circle of confusion. You can not separate Olive's conclusions from his test tracks and their SPL playback

1 hour ago, mitchco said:

 

While it would be nice if all speakers are well designed with rooms with favorable low frequency distribution of room modes and the right amount of diffusion and absorption. But for most of us, the reality is far from ideal. So we find and use the best tools available to deal with the reality. The reality is that for my clients that have compared partial corrections versus full range corrections (i.e. think tone control in the mids and highs = full range correction), over 95% choose the full range correction. 

 

Folks do have preferences when it comes to tonal response. Some like a bass bump, some like to tilt down the high frequencies a bit more than others. It is not about one size (i.e. target) fits all. It is about what one prefers while at the same time taking care of room modes and making the frequency response from both (or MCH) speakers equal so that there is actually a rock solid phantom center image. Smoothing the bass response so it is even and clear sounding. Make the timing response so all direct sound arrives at ones ears at the same time to improve the imaging. And have the timing response of each speaker the same over time, so that the depth of field opens up in a way most folks have not heard before. But I am biased :-)

 

I'm lucky I own active speakers that once were top of the line in finest broadcasting or recording studios. OTOH it's F1 and you can't run them with diesel (the settings and upfront I mean ; as of music it most always sounds gorgeous, I don't specialise at all in audiophile recordings). Whatever people do to make the system they could afford sound pleasurable is highly respectable. And that might account for "preferences" and choices of trade offs. However, I don't believe as much in such things as in adjustments to program materials via a set of in room responses "tone controlled". In exemple, I recently posted in Album of the evening that I listened, same evening, same physiological state, same system, first to MJ's Bad with massive bass boost (to fit a 1987 early digital Bernie Grundman's mastering) and then to classical piano recorded/mastered 2022 with flattish (even flat was fine) response. 

 

I see you take room dimensions in consideration in your work ; on that point I'm in total agreement ! Applying dimensions in the Virtual Bass Array Excel sheets offered by OCA to produce VBA filters (see : https://www.youtube.com/watch?v=q9aJqQpNyLY ) has truly been a step up 

 

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  • 2 weeks later...

I'd add one more device to the list of options - the Smythe Research Realiser A16.

Smythe focus on its unique ability to provide REAL immersive sound through headphones.

I can attest to its breathtaking realism through headphones once properly set up, although the setup requirement of a proper multiway HRTF is a considerable obstacle unless one already has a full surround or Atmos system.

 

In addition though, it is a full 24 channel Atmos/DTS:X etc decoder - and as well as the usual HDMI inputs has 16 inputs and 16 outputs. Depending on the version you get, these 16 in / 16 out are available in unbalanced (3.5mm TRS), Balanced XLR or Digital AES/EBU.

 

I have no connection to Smythe other than having purchased an A16 from them.

 

The hardware itself is excellent - and the headphone virtualisation spectacular, once you have your HRTF.

 

Having sung the praises of the Realiser A16, I have to say though that Smythe are one of the most frustrating companies I have ever dealt with. Emails and phone calls often go unanswered. They have no marketing to speak of - despite an excellent and unique product.

 

One upside though is that when they DO answer your call or email, they are extremely knowledgeable and helpful.

 

I get the feeling they are small team that are a) Overworked and b) more interested in the technology R&D than anything else.

 

But despite these negatives, I would still buy an A16 if I didn't have one. It's that good - and the headphone virtualisation is unique.

 

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6 minutes ago, asibbald said:

I'd add one more device to the list of options - the Smythe Research Realiser A16.

Smythe focus on its unique ability to provide REAL immersive sound through headphones.

I can attest to its breathtaking realism through headphones once properly set up, although the setup requirement of a proper multiway HRTF is a considerable obstacle unless one already has a full surround or Atmos system.

 

In addition though, it is a full 24 channel Atmos/DTS:X etc decoder - and as well as the usual HDMI inputs has 16 inputs and 16 outputs. Depending on the version you get, these 16 in / 16 out are available in unbalanced (3.5mm TRS), Balanced XLR or Digital AES/EBU.

 

I have no connection to Smythe other than having purchased an A16 from them.

 

The hardware itself is excellent - and the headphone virtualisation spectacular, once you have your HRTF.

 

Having sung the praises of the Realiser A16, I have to say though that Smythe are one of the most frustrating companies I have ever dealt with. Emails and phone calls often go unanswered. They have no marketing to speak of - despite an excellent and unique product.

 

One upside though is that when they DO answer your call or email, they are extremely knowledgeable and helpful.

 

I get the feeling they are small team that are a) Overworked and b) more interested in the technology R&D than anything else.

 

But despite these negatives, I would still buy an A16 if I didn't have one. It's that good - and the headphone virtualisation is unique.

 

 

Hi @asibbald, I kind of forgot about Smyth Research. After attempting to contact the company numerous times and hearing nothing in return, I gave up on it. 

 

I'd love to use the A16 with the Dante card to input encoded Atmos and output decoded Atmos as PCM over the network. 

Founder of Audiophile Style | My Audio Systems AudiophileStyleStickerWhite2.0.png AudiophileStyleStickerWhite7.1.4.png

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Yes, they are such a strange company! I sort of think of them as a research team that sells some stuff - sometimes - to cover their costs......

 

However, once you DO manage to get an A16, you'll be glad you persevered...There is nothing else like it on the market. The immersive audio, with full head-tracked HRTF is indistinguishable (to me) to listening to a full Atmos speaker setup. And it is a lot less annoying for the neighbours and the other half.....

 

Again, when you DO get their attention, they're great. I once returned my A16 to them for repair as I thought it had a problem. James Smythe checked it, confirmed there was no problem and returned it with no charge. Indeed, the "problem" was my setup of other devices - not the A16. But this anecdote illustrates the problem. Whilst it was lovely of James to return it with no charge, he really SHOULD have charged me for the time they spent investigating my silly error. How else will they be able to afford the people they need in Sales and Marketing? Any other company would have charged me a few hundred pounds, probably.....

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42 minutes ago, cpasmoi said:

Good morning

very interesting your article on the relevance of the processing upstream of the digital correction of the listening room
I invite you to use the Thierry Service from Home audio Fidelity, it seems to me that there is an article on Audiophile Style

 

https://www.homeaudiofidelity.com/

 

musically😀

 

Your welcome. I think you are referring to: 

 

Thierry has a good reputation, as does Mitch (who did the review linked above). So one can choose and will in both cases get an exceptional result.

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  • 1 month later...
  • 2 weeks later...

I'd add one more device to the list of options - the Smythe Research Realiser A16.

Smythe focus on its unique ability to provide REAL immersive sound through headphones.

I can attest to its breathtaking realism through headphones once properly set up, although the setup requirement of a proper multiway HRTF is a considerable obstacle unless one already has a full surround or Atmos system.

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  • 2 weeks later...

From what I've seen in the marketplace (MiniDSP, DSPeaker, etc.), most room correction DSP is done at 24/48 or 24/96 (my Lyngdorf TDAI-1120 resamples everything to 24/96). How does one rationalize that resampling against the desire for high quality DSP (say via Roon or HQPlayer). If the DSP occurs before a stand-alone DAC, the DAC is receiving a "bastardized" signal from the DSP unit. If the DSP occurs after the DAC, the DSP is changing the result of the DAC's work.

 

I'm really struggling with this as I'm trying to design a system that incorporates room correction (I'm currently using convolution filters in Roon to good effect), bass management (I run a 2.2 stereo system and my subs don't have a HP pass-through), and an external DAC so I can use Roon/HQPlayer...I purchased a lifetime Roon license when Roon first launched.

 

I know I can load FIR filters in HQP, so I could move that function from Roon to HQP. I also believe there's a way to handle bass management in Roon using Procedural EQ, but I have no idea how to accomplish that and there isn't any type of guide available. Roon provides for speaker distance entries, but only for the mains, not the subs. There are a couple of analog crossover products available from Behringer and DBX, but I've read that they're noisy.

 

A MIniDSP or DSPeaker solution would be easy single box solutions, but they wouldn't be my first choice for audio quality. A solution using HQP and/or Roon would be preferable (I think).

 

Thoughts/input?

 

 

Under construction.

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23 minutes ago, catastrofe said:

From what I've seen in the marketplace (MiniDSP, DSPeaker, etc.), most room correction DSP is done at 24/48 or 24/96 (my Lyngdorf TDAI-1120 resamples everything to 24/96). How does one rationalize that resampling against the desire for high quality DSP (say via Roon or HQPlayer).

Here's how.  Does the improvement due to DSP room correction outweigh the potential loss due to downsampling?  In my experience, it generally does.  BTW, you can run Dirac at 24/192 and there's little issue with using that, again, imho.

Kal Rubinson

Senior Contributing Editor, Stereophile

 

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4 hours ago, catastrofe said:

From what I've seen in the marketplace (MiniDSP, DSPeaker, etc.), most room correction DSP is done at 24/48 or 24/96 (my Lyngdorf TDAI-1120 resamples everything to 24/96). How does one rationalize that resampling against the desire for high quality DSP (say via Roon or HQPlayer). If the DSP occurs before a stand-alone DAC, the DAC is receiving a "bastardized" signal from the DSP unit. If the DSP occurs after the DAC, the DSP is changing the result of the DAC's work.

 

I'm really struggling with this as I'm trying to design a system that incorporates room correction (I'm currently using convolution filters in Roon to good effect), bass management (I run a 2.2 stereo system and my subs don't have a HP pass-through), and an external DAC so I can use Roon/HQPlayer...I purchased a lifetime Roon license when Roon first launched.

 

I know I can load FIR filters in HQP, so I could move that function from Roon to HQP. I also believe there's a way to handle bass management in Roon using Procedural EQ, but I have no idea how to accomplish that and there isn't any type of guide available. Roon provides for speaker distance entries, but only for the mains, not the subs. There are a couple of analog crossover products available from Behringer and DBX, but I've read that they're noisy.

 

A MIniDSP or DSPeaker solution would be easy single box solutions, but they wouldn't be my first choice for audio quality. A solution using HQP and/or Roon would be preferable (I think).

 

Thoughts/input?

 

 

I recommend state of the art DSP for room correction. I can run 12 channels of DXD (24/352.8) at native rate with room correction, no problem. 
 

 

Founder of Audiophile Style | My Audio Systems AudiophileStyleStickerWhite2.0.png AudiophileStyleStickerWhite7.1.4.png

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4 hours ago, Kal Rubinson said:

Here's how.  Does the improvement due to DSP room correction outweigh the potential loss due to downsampling?  In my experience, it generally does.  BTW, you can run Dirac at 24/192 and there's little issue with using that, again, imho.

 

1 hour ago, The Computer Audiophile said:

I recommend state of the art DSP for room correction. I can run 12 channels of DXD (24/352.8) at native rate with room correction, no problem. 
 

 

 

Thanks Kal and Chris.

 

Kal, you make a good point regarding the value of room correction superseding the perceived disadvantage of downsampling. What hardware supports Dirac Live at 24/192? 

 

Chris, similar question...how are you running DXD with DSP at its native rate? HQPlayer?

 

Thanks gents!

Under construction.

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