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Topics - Tranquility Bass

#1
There is a school of thought that says the only way to accomplish a linear phase crossover is to use linear phase filters which are a special class of FIR filter that sums to a unity response with a fixed time delay. So when both high pass and low pass sections are added together the response is a delayed version of what is being fed into the crossover. As I have discussed in another thread this type of filter has issues with proper impulse response cancellation due to imperfect matching between drivers which can result in severe pre-ringing leakage among other topics. The proponents of these filters will never talk about this aspect of this type of filter topology, instead pretending that it doesn't exist or can easily be minimized so that it is never a problem.

The other way of linearizing the crossover is to take an existing non-minimum phase crossover and apply a global group-delay correction filter which is just an FIR filter with a large number of taps. The advantage here is there are no FIR filters in the actual crossover to generate any pre-ringing artifacts. This is the approach taken by a few commercial designs as well as here, although the correction filter usually requires a large number of taps and has a large delay depending on the sampling rate and tap count. So this should be taken into account if you want to use these speakers with other speakers or in conjunction with a video display in say a home theater system in order to avoid lip-syncing issues.

We took a four-way 8th-order Linkwitz-Riley crossover from one of our clients who own one of our Preamps and applied a global group-delay correction filter to linearize the phase response. The LR crossover was already flat but the phase response was anything but linear so a square wave fed into it did not look like a square wave coming out of it. A linear phase response means that there is just a time delay in the signal path whilst still maintaining a flat magnitude response but there is no waveform distortion.

To measure the phase distortion of the crossover in isolation we needed to sum the outputs of the crossover before they were level adjusted and time delayed so we could focus on the crossover alone without the effects of the speaker and the room etc which we know adds its own artifacts to the response. Later on, we will look at compensating for those as well but for now we are just focussing on fixing up the crossover and making sure the group-delay correction filter is doing its job properly.

To evaluate the crossover we just looked at one channel and summed the outputs to measure the net frequency response. We also fed the input to the crossover to one of the outputs of the preamp as a reference for the analyzer to create the frequency response. The summed outputs of the crossover are fed to another channel on the preamp. We also added a few multiplexers or selector switches to enable us to switch in and out various filters quickly so we can quickly evaluate the effects of different filter configurations. Both the input to the crossover and the summed outputs are then connected to our dScope III audio analyzer. The dScope III can measure both amplitude and interchannel phase. The following Audioweaver test bench is what we used to evaluate the effectiveness of the global correction filters.

Xover-Test Bench1(AWD).png

All of the DSP is done on a PC instead of the Preamp itself because the group-delay correction filters required are beyond the resources of the onboard SHARC DSP. The Ultimate Preamplifier Plus (UPP) has a unique feature in that it allows one to run DSP on an external device such as a PC as though it was running inside the Preamp. In fact, in another thread, we proved that the audio path was transparent and the performance of the Preamp was unaffected by the noisy environment of a PC ! The Ultimate Preamplifier Plus can also share DSP between its own onboard DSP as well as an external PC so for example you could build a non-minimum phase LR crossover using the onboard SHARC DSP whilst running the correction filter on an external PC and then switch the correction filter in or out from the Preamp menu. This is the approach our client is taking but for proof of concept and convenience, we ran everything on an external PC which allowed us to quickly evaluate and test everything in the one environment. The main aim was to validate the effectiveness of the global group-delay correction filters and prove that you don't need to use dedicated linear-phase filters to achieve this.

First, we measured the frequency and phase response of the crossover filter alone using a log frequency axis. We note the flatness of the filter as expected but the phase is anything but flat ! The top blue trace is the sweep of the input which is ruler flat as expected and the bottom red trace is the crossover summation of all drivers which is also ruler flat as expected.

Xover-4way(for testing)(FR).png

To evaluate the phase response we reran the frequency response test using a linear frequency axis instead of the usual log axis. If the phase is linear then the phase response should look straight and not curved. Since the analyzer cannot distinguish phase greater or less than 180 and -180 degrees respectively it wraps or folds the phase so the response always is contained within a 360 degree envelope which makes it look like a saw-tooth. From the phase plot below we can see the phase is anything but linear which was expected !

Xover-4way(for testing)(PHASE-without phase correction).png

And now for the money shot. What does this crossover filter do to a square wave? The square wave is important because it is not just a single tone but rather a series of odd harmonically related tones with a monotonically decreasing magnitude. If the phase is not linear, it will manifest itself as distortion in the waveform even though the magnitudes of the harmonics are still correct. So, let's look at the test results on a scope.

Firstly at 1kHz and then at 100 Hz !! This is what a non-minimum phase crossover does to a square wave !! Can we fix this ??

Xover-4way(for testing)(SCOPE-without phase correction).png

Xover-4way(for testing)(SCOPE-100Hz SQWAVE-without phase correction).png



#2
The following Jitter tests illustrate the benefit of using the built-in Inter-sample Overs Guard in preventing internal numerical overflow inside the asynchronous sample rate converter of the SHARC DSP. We used the same J-test methodology that we used for our other tests.

Firstly the following shows the scope screen capture of one channel of the output of the Preamp with the J-test signal from the analyzer applied directly to the USB port of the Preamp. For all intents and purposes, it should look like a 12kHz sinewave but because of Intersample Overs, there is internal overflow in the sample rate converter which manifests itself as waveform distortion similar to clipping which is a side effect of upsampling or interpolating to a higher sampling rate.

J-Test_Waveform(SRC-USB).png

The following shows the resultant FFT spectrum and notable artifacts can be observed.

J-Test(SRC-USB+NO IS Guard).png

Expanding the frequency scale of the spectrum above shows in much more detail the problems caused by the inter-sample overs.

J-Test(SRC-USB+NO IS Guard-expanded).png

With the Inter-samples Guard switched on we noted how many times the sample rate converter was overloading in the statistics collecting mode ! Once activated the Guard reduced the signal input level to avoid any more internal arithmetic overflows and reported that the signal had to be reduced by 3dB to achieve this.

ImportedPhoto_1736826332305.jpeg

And the signal from the output of the Preamp was reduced in amplitude by 3dB but is no longer visually distorted!

J-Test_Waveform(SRC-USB+IS Guard).png

Now let's see the effect on the J-test spectrum from the analyzer. A vastly much improved and cleaner spectrum is observed below when the sample rate converter is not overloading and essentially proves how transparent the SHARC sample rate convert is !

J-Test(SRC-USB+IS Guard).png

The expanded frequency scale of the above FFT spectrum is shown below !

J-Test(SRC-USB+IS Guard-expanded).png


#3
Someone emailed me recently after I posted the results of routing digital audio through an external PC for the purposes of expanding the DSP capability of the Ultimate-Preamp and asked whether or not using a PC adds any additional noise, distortion or jitter to the audio stream ? Well I said in theory it shouldn't due to the isolation and transparency provided by this interface but there is only one way to find out and that is to measure it.

So using the same J-test methodolgy that we used for the normal jitter tests on the various inputs to the preamp we can now apply the same test methodology whilst routing the audio through an external Dell PC used in our lab and see how it affects the jitter and noise. So we setup Audioweaver on a PC to process audio from the Preamp at 192kHz in a direct input-to-output connection as in the following:-

Setup for J-Test on PC.png

Then we measured the jitter from the output of the Preamp using the same J-test methodology as we used on earlier tests of jitter.

J-Test(SRC-USB+IS Guard+2x8-Channel via PC).png

The screenshot below is the same as above but with an expanded frequency scale. As can be seen the spectrum is as clean as it is with internal DSP processing and any artifacts are way below the threshold of hearing !

J-Test(SRC-USB+IS Guard+2x8-Channel via PC-Expanded).png

We did the same for THD+Noise.

THD + N.png

As can be seen in the test results above the PC is essentially transparent to the audio stream and does not add any noise, distortion or jitter to the incoming audio stream thanks to the hardware of the Ultimate Preamplifier Plus. This is contrary to the reputation of PC's as a noisy and hostile environment due to high speed digital design along with a switching power supply not optimized for low noise. However, the UPP mitigates these issues with ease. In other words don't waste your money with fancy re-clockers and FIFO's because the Ultimate Preamplifier does it all for you and the test results above speak for themselves ;)

https://analog-precision.com/forum/performance-and-measurements/jitter-tests/

https://analog-precision.com/forum/performance-and-measurements/thd-n-balance-output/

.

#4
Hate to break the bad news !!

#5
News Updates / Vinyl sound quality myth destroyed ??
January 05, 2025, 06:48:27 PM
Not as simple as the more expensive turntable the better !!



#6
A great read for anyone interested or skeptical of class-D amplifiers ;)

LIFE ON THE EDGE – A PERSONAL PERSPECTIVE ON THE PAST, PRESENT, AND FUTURE OF CLASS D AUDIO AMPLIFIERS

BRUNO PUTZEYS OCTOBER 22, 2024 30TH ANNIVERSARY THE NOW
#7
Lately, I have been seeing more and more Facebook ads from local vendors. Obviously, the Facebook algorithm determines that I am local and what interests I have so it knows which ads to display on my feed. Some of these local audio vendors used to be sponsors on that you-know-what over-saturated, highly restricted, over-censored, intentionally suppressed images, highly manipulated, expensive and ineffectual forum until they could see the writing on the wall ! Now they are popping up on my Facebook feeds and undoubtedly others interested in this area. Could this be a trend for other local vendors and manufacturers? Hmmm, only time will tell, but the important thing here is that no one person with ulterior motives for a grab for money is manipulating their outcomes by playing one vendor off against another. All done with clever algorithms ;)

The list just keeps getting bigger and bigger by the week !!

Koala Audio.png

The Audio Tailor.png

RIO Sound and Vision.png

AudioTrends.png

CableTieCompany.png

SoundsEasy.png

TitanAV.png

HiFiHQ.png

Tivoli Hifi.png

Monitor Audio on FB.png

Marco Custom Cables on FB.png

CHT Solutions on FB.png

NB Audio on FB.png

Addicted to Audio on FB.png

#8
News Updates / Latest Firmware Update - 240805-1507
August 05, 2024, 07:32:50 PM
Please click on the following link for the latest firmware updates for the UP1,UP2 and UPP. (You need to be a registered member of this forum to access this page.)

https://analog-precision.com/forum/firmware-updates/firmware-update-24/
#9
Please click on the following link for the latest firmware updates for the UP1,UP2 and UPP. (You need to be a registered member of this forum to access this page.)

https://analog-precision.com/forum/firmware-updates/current-firmware-update/
#10
For those fake review websites and infuencers that keep promoting "audio-file" network switches please get your facts straight and stop spreading mistruths and propaganda just because it is profitable for you to do so. That is no excuse to do it.

Unlike these fake reviewers and as someone that has actually designed DAC and DSP hardware all I can say is that once those 'ones' and 'zeros' are re-assembled inside a buffer within a DAC or DSP, the electronics does not care where they came from. Whether it's an S/PDIF, Toslink, USB or ethernet connection via streamer and network switch etc it makes no difference to the DAC hardware how they got there as long as there are no errors in the data then each source will produce an identical result and this can be measured as well !

And there in lies the rub. These fake review websites rarely measure anything if at all. Instead they will come up with a whole lot of lame excuses as to why they should not measure anything which is contrary to the people who design the hardware and/or the silicon used in most modern electronic devices. None of their lame excuses stands up to any scrutiny which should be a red flag to anyone reading it. What these people are doing is sending the industry back to the dark-ages and promoting a whole new industry of snake-oil merchants, snake-oil products, scam artists and spivs.

The only caveat here is that different devices may use different levels of isolation with the possibility of passing noise into the connecting device. However this all should be clearly measurable but of course if you don't measure anything then how would you know ? Of course this aspect which is usually the focus of most of these fake reviews has no bearing on the end sound quality. And changes in someones subjective interpretation of sound-stage is certainly not a reliable performance metric !!






#12
Don't be fooled by the blurb on the DEQX website regarding group-delay correction or compensation of loudspeakers. It's a way of oversimplification of reality and they have been pushing the same barrow for decades which is probably why they have never commercialized their own speaker systems using it, instead pushing the gimmicks onto other naive loudspeaker designers. Trying to fix up a loudspeaker on a single axis was never going to work. Loudspeakers are far more complex than this and radiate into free space in all directions and not just on one axis alone! It's easy to apply an inverse convolution filter to some point in space and say "can you hear the difference ?" but is it an improvement or a step backward towards ultimate accuracy in a practical listening environment ?

Group Delay Correction.png

What would fix up a signal chain on an electrical connection simply won't work with a distributed device such as a loudspeaker. This is why no serious high-end audio manufacturer would ever use a DEQX! Yes, sure our own  UPP can do long-length high sample rate, ultra-deep convolution, and FIR filtering and do a much higher resolution correction than a DEQX could ever do but do you really want to go down this path?  When it comes to loudspeakers there simply is no free lunch here and no easy fix and throwing lots of DSP at the problem can often make the problems a lot worse. It certainly is not a panacea for a bad speaker design to begin with!

Anyway don't take our word for it but we suggest you read these three important documents below before outlaying your hard-earned money on such a device or anything that is just a fancy inverse convolution filter ! These are documents written by other well-established audio engineers and echo the same sentiment as us. They tell a completley different story to what DEQX does. This is what DEQX will never tell you and why they never sell loudspeaker systems themselves using their own DSP hardware and even if they did it was always going to be a band-aid solution to a complex problem ! It all boils down to who are you going to believe ? These well-respected eminent audio and electrical engineers or some marketing hacks trying to jump on the DSP bandwagon whilst telling everyone how they should be designing speakers !

https://www.grimmaudio.com/wordpress/wp-content/uploads/speakers.pdf

And the take-home message from this document is:-

QuoteDSP loudspeaker crossovers done right

From the above we've learned that:-

• Heavy-handed correction exacerbates acoustical problems
• Sharp, linear-phase filters cause pre-ringing
• Targeting an exact linear-phase sum can cause pre-echos.

In short, brute-force correction sounds grainy and smudgy. When you hear cymbals go "splash" instead of
"crash", it's naive DSP at work. So:-

• Do not shave off the hair, a nasty stubble will grow back.
• Do not correct beyond the very beginning of the impulse response.
• The gentler you correct, the wider the angle over which the correction still improves things.
• Target a minimum phase sum.

For the time being I would strongly recommend designing the correction manually. This rules out FIR as the
main workhorse. For each bump or dip one corrects, one should know exactly where it comes from, and make
sure that it isn't better corrected for acoustically. Unfortunately, designing DSP filters does not relieve one from having to know one's acoustics.

Also:-

https://linea-research.co.uk/wp-content/uploads/LR%20Download%20Assets/Tech%20Docs/CrossoverFilters%20White%20Paper%20-C.pdf

QuoteAlso shown in Figure 8 is the impulse responses for a complementary high-pass brick-wall FIR. If we construct a crossover filter bank with such a complementary pair of filters, the Gibbs ripples are also complementary (since we will expect the filters to sum to a flat response with linear phase, producing a perfect impulse). The summed result will thus be free of any Gibbs ripple, so what's the problem? The problem is off-axis. The complementary ripples will only cancel if the delay suffered by the signal from each driver is identical. Off-axis, where the path lengths differ, the ripples will not cancel, leading to the possibility that Gibbs ripple might become audible (just like a high-Q ringing filter).

Such summing errors will be more pronounced at higher crossover frequencies because the ripples are more closely spaced. Lower frequency
crossovers will have wider ripples which will more easily cancel in the presence of off-axis induced delays.

It is evident that steeper cut-off slopes give rise to Gibbs ripples of greater duration. It makes sense therefore to restrict the cut-off slope to be no more than is necessary for the application.

And from the Linkwitz Lab website pretty much the same cautionary tale ;)

https://www.linkwitzlab.com/frontiers.htm

QuoteI - Digital crossovers

Some people think that digital crossovers will replace analog ones, because digital filters can be designed with desirable characteristics that are impossible to realize with analog circuitry. In particular, lowpass and highpass filters with extremely steep slopes and linear phase shift are possible. Steep slopes reduce the overlap region between drivers. Linear phase shift eliminates waveform distortion and merely causes a delay of the signal.  Such characteristics can be obtained from the digital equivalent of tapped delay line filters, which have a finite impulse response (FIR) duration that depends upon the number of taps used. Digital FIR filters can have almost any desired frequency response, if the number of weighted taps is made sufficiently high. [1]

The linear phase shift comes at a price. The impulse response rings. The more so, the steeper the filter slopes. Both lowpass and highpass sections of the crossover ring, but when the outputs are combined, as for a crossover, then the two impulse responses add to a non-ringing, delayed pulse.

All would be fine, if we listened only in anechoic spaces or to speakers with coincident drivers. In reality we use speakers in rooms with reflections and reverberation and the the drivers are separated from each other due to their sizes. As a consequence the off-axis response of the speaker matters and contributes to what we hear. With the drivers non-coincident, the lowpass and highpass outputs are delayed different amounts at points off-axis, and the ringing is no longer canceled in the addition. In the best case the drivers might be coaxial, but this has another set of problems. Very steep crossovers can also cause a very abrupt change in the polar pattern of the speaker, when transitioning from a large diameter driver to a small one. Under reverberant conditions and/or listening off-axis this may have audible consequences.

And the proof is in the eating of the pudding. If linear-phase filters were all they were cracked up to be then Linkwitz would have incorporated them into his LX series open baffle designs and yet he settled on a standard crossover design implemented using either analog or digital IIR filters. There are no FIR filters in his designs ;)
#13
Cantata / Technical Information/Crossover Schematics
January 08, 2024, 10:54:53 AM
Please feel free to add any technical material you may have on these speakers.
#14
Millenium / Reviews
January 08, 2024, 10:36:04 AM
https://www.audioasylum.com/messages/speakers/48322/review-dunlavy-audio-labs-millennium-speakers-review-by-brian-a-at-audio-asylum

QuoteAfter many months of research I went with these speakers for the following reasons.
Extreme tonal accuracy, +/- 1dB from 20Hz to 20KHz.
Non-ported enclosure for clean bass.
Fabric dome tweeter for smooth treble.
Phase/time aligned for accurate transient reproduction.
Non-parallel cabinet walls to minimize internal standing waves.
Quick signal drop off in waterfall plots.
Clean pulse and step response.
Auditioned them and enjoyed the best sound I have ever heard!

It is hard to describe these speakers for I believe they are pretty much fully accurate and transparent. They totally disappear when playing despite their 76 inch height and 300 lbs. each weight. When you slip in a SACD/CD the wall dissapears and becomes a music stage for the musicians. Others have noticed this too and are quite dissapointed when they get home only to find their speakers don't do the disappering act, you can hear where each speaker is. Dunlavy's are matched to withen 0.5dB of each other to ensure this.

These speakers have a certain cleanness and accuracy that is very hard to describe. When I was at the factory in Colorado springs and did A/B comparisons with other Dunalvy speakers these just sounded more open. It was like the band was in the open, on a hill outside or something. With the other speakers, though they sounded great, the music was slightly veiled. I believe this is born out by the waterfall plots of the Millenniums, very clean and quick decay.

The soundstage of these is excellent. With some source material you can hear sounds coming from beyond the left and right of the speakers. Instruments are accurately placed across the area between, and beyond, the speakers. The speakers totally disappear, when the singer and drums are between the speakers, that is where the sound is, you don't hear any sound from the speakers themselves. The sweet spot is only wide enough for one though. However, anywhere in the room the sound is tonally balanced and enjoyable, you just don't get that nice balanced imaging you do in the middle. This is what totally turned me off of planer speakers, their horrible off axis tonal balance, and their laughable bass for that matter.

Perhaps the most noteable aspect of the Millenniums is there stupendous bass. It is so clean you sometimes think its lacking. There is absolutely no boom, overhang, thump, or distortion, even at high levels. I must admit I am used to hearing the 100Hz hump on most cheaper speakers that simulate a good bass response. I notice songs sound different. The bass is very clean and deep too. You can feel deep bass that you couldn't with lesser speakers. Lest you think these speakers are lacking in bass, if you play a song that truely has bass, these will reproduce it in spades. It is just amazing to listen to songs and for the first time hear and feel the bass/drum line of the song very cleanly. There is lots more detail and nuances to be found in the deeper few octives of music than I was aware of before.

The mids are flawless too. Voices are clean and undistorted. Dianna Krall sounds fabulous. Here music with the bass and piano sounds simply stunning. Celine Dion sounds excellent too. The harshness and forwardness of her voice is subdued to some extent, more enjoyable. Though with some of her songs, let's face it, she's really hollering. Men's voices also are nice, never nasally or boomy, always clean.

The treble is so clean and accurate, it captures the metalic sheen of cymbols and other metalic instruments but you need SACD to really enjoy this. There is no brightness, exageration, or harshness to be found, unless it is in the recording. When I compare the treble of these to that of my Paradigm Studio 100's in the home theater room, there is no comparison. Fabric dome tweeters are some much cleaner than metal domes, more natural and enjoyable.

The speakers themselves are a joy to look at. Their looks really grow on you. You start to appreciate their unique hourglass shape. It is so gracefull. My wife, who about flipped when she first say them, way too big and ugly as sin. Now she likes their looks. When we have visitors the women are usually amazed my wife allows me to have them. All the guys drool. You can tell there is some prime sound able to be produced by these massive transducers. The speakers are actually larger than I am, I'm 6-3 and 250 lbs. The speakers have an inch and 50 lbs on me. My son calls them the speaker gods.

About the only thing I can say bad about them is how they reveal poor recordings. Imagine my dismay when two of favorite groups as a teenager have some bad recordings, Fleetwood Mac and Abba. I love listening to SACD music with these. Horns and violins are richer and not strident as they can be with normal CD's. Cymbols are more metalic. The soundstage is enhanced.

Is this the perfect speaker? Probably not, but I am very happy with it. To me it sounded even better than Dunlavy's top of the line SC-V and SC-VI's. For someone with some money to burn, fly out to Colorado and listen to them for yourself. I don't think any dealer carries these for demos.

Read up on the manufacturer's website for the theory behind these speakers. The time alignment of the drivers, the hourglass shape etc. It is www.dunlavyaudio.com. Good reading.
#15
News Updates / The new Dunlavy/Duntech Archive Forum
January 03, 2024, 09:24:41 AM
This forum was created in remembrance of the late John Dunlavy and his contribution to both the art and science of audio reproduction which has lived on in many of the loudspeaker systems that he created over the decades and are still being used today. Not only that many of the original concepts developed by John Dunlavy such as baffle felt have been used by many other speaker designers with little or no credit given back to John.

Click here to view the all new Dunlavy/Duntech Archive Forum

sovereign-diagram.fw.png
#16
News Updates / We are moving to new premises !
January 01, 2024, 10:06:49 AM
We have moved to much larger new premises in the last month which has been a mammoth task. Now need to unpack everything and set up the lab again. Now we have twice as much area as before and no more distractions which has put us out of action for quite a while now :(

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#17
Athena / Model Information
October 29, 2023, 07:13:22 PM
Waiting for more data !
#19
Sovereign 2001 / Brochures
October 29, 2023, 05:26:57 PM
#20
Sovereign 2001 / Websites of Interest
October 29, 2023, 05:24:17 PM
https://classic-hifi.net/product/duntech-sovereign-2001/

https://web.archive.org/web/20040906211613/http://www.apogeespeakers.com/reviews/a_search_for_the_ultimate_speaker_bestofaudio.htm