[Siz.]

Interesting - thanks @JaZZ Would that be expected that the filters wouldn't change going from 96 kHz -> 192 kHz? I'd be curious to know what happens at 705.6 kHz and 768 kHz.

The anti-aliasing filtering may be different going from 96 kHz to 192 kHz, as the higher Nyquest frequency allows gentler roll-off. But I don't see any reason for the colored user-selectable filters to behave differently, as they act on frequencies in the audible range, far below the Nyquest frequencies. This seems to be consistent with the graphs.

 

[JaZZ]

The anti-aliasing filtering may be different going from 96 kHz to 192 kHz, as the higher Nyquest frequency allows gentler roll-off. But I don't see any reason for the colored user-selectable filters to behave differently, as they act on frequencies in the audible range, far below the Nyquest frequencies. This seems to be consistent with the graphs.

I also believed that a sampling rate of 96 kHz or at least 192 would possibly make the antialiasing filter less critical. While that may be the case in terms of aliasing, Rob has explained that in the function of a «reconstruction filter» the WTA filter still makes a considerable difference with hi-res recordings as well. Something I can easily reproduce with the M Scaler now.

I agree that the stereophile graphs are misleading, but the sharpness of both the 96 and the 192 kHz filters at their Nyquist frequency is mentioned in the text – and the WTA filter is sharp and steep by default. The task of the HF filter is suppressing ultrasonic interferences which may occur at high sampling rates, according to Rob.

 

[Rob Watts]

Bump on this question... Can anybody (Rob?!) tell me what, if anything, changes in the anti-aliasing filters on the Qutest (and/or Hugo 2) when being fed different sample-rate inputs?

The WTA1 filter, which is used for 44.1 to 384k, has no change at all whilst going from 44.1 to 48k - it's merely the same filter run at a slightly different rate. But when you double the sample rate, then WTA1 goes into a double mode - so it's the same characteristic, but half the rate, as the input rate is doubled. In effect. 20 kHz becomes 40 kHz for 44.1 to 88.2.

For 705/768 WTA1 is in pass through mode, so it's not filtered. After WTA1 you have two choices - either WTA2 (which is a linear phase symmetrical WTA filter that takes you from 16FS (786 kHz) to 256 FS (12,288 kHz or 12.288 MHz) - the white and green filter - or an IIR filter. This 3 stage IIR filter either starts at 256FS (white or green) or takes over at 16FS to replace WTA2 (orange or red). The time constants for this filter is adjustable (about 240 kHz or 60 kHz) and this gives us the high frequency filter (white/orange off, green/red on). The intent on this filter is to remove the ADC distortion and noise that plagues HD recordings.

The HF filter is easily measurable - its about -1dB at 20kHz. The 16FS or 256FS is NOT measurable using standard tests, as it only affects above 352 kHz, and its subtle. It was a big surprise to me however, in that how audible the 16FS/256FS WTA2 filter actually is.

As too the Stereophile frequency response test this is actually incorrect. Qutest certainly does not drop like a stone above 19.5 kHz. This is because the WTA1 latency is so large, you can't use AP standard FR tests, as the latency makes the AP record the incorrect output. The actual frequency is at 21,990 Hz for 44.1 kHz. The noise plot is correct, as this test is latency independent.

 

[Toyboyo]

Hi Guys

Been through some interesting times last couple of weeks. My normal store did not stock Chord gear so I went to another retailer I know, but then I heard pretty close to the final version of my new speakers and they will be costing even more than the maker thought because he also needs to build a uber stand. To ensue I do not run out of money I reluctantly had to cancel my order. Then my normal retailer contacted me and said he can get the Chord stuff in and I can fix him up money wise when I fully pay for the new speakers - I have already paid a lot of the cost of the new speakers - so great - I can get TT2 and M-Scaler.

They arrived, but the guy at my normal store is really busy so the technician I know who works up the road picked it up. He will build the initial cables etc. As a normal DA he was MIGHTY impressed - his exact words - very sweet.. He didn't try the M-Scaler because he needs a pair of BNC connectors (some may already be in the M-Scaler box - he hasn't opened the box yet). He wasn't connecting to the speakers direct yet - he wants build a 4A power supply before trying that (see below)..

Interestingly he tried a power supply he makes (it does 1 amp) and thought it better. Strange - he has read all of what Rob has written about the power supply and could not figure out why. Anyway he contacted me and asked would it be OK to build a 4A one - I said OK so we will see. Will try one on the M-Scaler as well.

A couple of issues for Rob:

1. He uses an Aurilac Aries as a source and at first just got junk out of it. He shut it down then started it up and it seemed to work OK.

2. Where are the huge capacitors in the TT2 - in the DAC case or the SWPS you plug into it? If its in the SWPS then my tech is really scratching his head - it should not have made the difference he heard - they should have stopped any hash from the SWPS - if its in the DAC itself then there may be some SWPS hash may radiating in the case.

Altogether very encouraging and interesting. But the tech has to find time from his normal work to build the cables - so more to come when cables built etc.

Thanks
Bill

Makes me want to come up to the GC for this!!!
I would love to hear the same test with an Mscaler to the Dave (instead of Blu with Ferrite on the BNC leads!!!!)

 

[bhobba]

Makes me want to come up to the GC for this!!!
I would love to hear the same test with an Mscaler to the Dave (instead of Blu with Ferrite on the BNC leads!!!!)

Me to. Since I posted that I broke my Distal Femur. It's 12 months to heal so me mucking around with my TT2 and Mscaler is out for quite a while. I have lent it to some friends but they are all busy and checking stuff out has ground to a halt. Ah well - that's life.

Thanks
Bill

 

[Toyboyo]

The WTA1 filter, which is used for 44.1 to 384k, has no change at all whilst going from 44.1 to 48k - it's merely the same filter run at a slightly different rate. But when you double the sample rate, then WTA1 goes into a double mode - so it's the same characteristic, but half the rate, as the input rate is doubled. In effect. 20 kHz becomes 40 kHz for 44.1 to 88.2.

For 705/768 WTA1 is in pass through mode, so it's not filtered. After WTA1 you have two choices - either WTA2 (which is a linear phase symmetrical WTA filter that takes you from 16FS (786 kHz) to 256 FS (12,288 kHz or 12.288 MHz) - the white and green filter - or an IIR filter. This 3 stage IIR filter either starts at 256FS (white or green) or takes over at 16FS to replace WTA2 (orange or red). The time constants for this filter is adjustable (about 240 kHz or 60 kHz) and this gives us the high frequency filter (white/orange off, green/red on). The intent on this filter is to remove the ADC distortion and noise that plagues HD recordings.

The HF filter is easily measurable - its about -1dB at 20kHz. The 16FS or 256FS is NOT measurable using standard tests, as it only affects above 352 kHz, and its subtle. It was a big surprise to me however, in that how audible the 16FS/256FS WTA2 filter actually is.

As too the Stereophile frequency response test this is actually incorrect. Qutest certainly does not drop like a stone above 19.5 kHz. This is because the WTA1 latency is so large, you can't use AP standard FR tests, as the latency makes the AP record the incorrect output. The actual frequency is at 21,990 Hz for 44.1 kHz. The noise plot is correct, as this test is latency independent.

Great explanation - I am the new owner of a Qutest and a DAVE and this helps!!
A couple of questions:
1. Does the DAVE behave in a similar fashion - except there is only the HF filter?
2. If we miss the WTA1 filter with upsampling does this not undo the advantage of your programmed sound?

 

[bhobba]

Well the friend I lent the DAC to finally connected into his system.

To start with it was connected very simply, just using the SPDIF output from a CD Player and the RCA audio outputs in low gain mode - no Mscaler at the moment. Already, and this person has had a lot of different gear in his system over the years, he can say its an exceptionally good sound - a lot of very good ability to pinpoint instruments etc and great body to the sound. His wife in particular thinks it sounds just wonderful. Its just an initial listen, and may change with burn in.

Just one issue - the right channel RCA output is noisy. Any ideas anyone? The tech I originally lent it to didn't say anything about that - but he would have used USB - not SPDIF.

Thanks
Bill

 

[Rob Watts]

Great explanation - I am the new owner of a Qutest and a DAVE and this helps!!
A couple of questions:
1. Does the DAVE behave in a similar fashion - except there is only the HF filter?
2. If we miss the WTA1 filter with upsampling does this not undo the advantage of your programmed sound?

Yes Dave is the same but no option to lose WTA2. The idea of switching out WTA2 is the transient timing uncertainty that happens without the WTA means it sounds softer due to the errors; at Dave's price point you should not need artificial softness, as quality transducers (one hopes!) would be employed.

All the up-samplers I have seen either have insufficient taps, or do not have WTA like algorithms; in short they have much more transient timing errors and so will sound unnaturally soft, with poorer imagery, timbre variation, pitch and tempo perception.

 

[bhobba]

Hi All

The right output is now totally kaput - its more than just noise evidently - its making crackling sounds as well - i was told like a faulty valve. Have to return it for service so having some friends check it out will have to wait. Bummer.

But the guy checking it out was curios as to the best method of connecting his CD transport to the DAC - anybody have any experience with this?

And just to be certain is using pin 2 and 3 the best way to connect to the speaker - I asked before but the person checking it out wants to be careful.

Thanks
Bill

 

[csglinux]

The WTA1 filter, which is used for 44.1 to 384k, has no change at all whilst going from 44.1 to 48k - it's merely the same filter run at a slightly different rate. But when you double the sample rate, then WTA1 goes into a double mode - so it's the same characteristic, but half the rate, as the input rate is doubled. In effect. 20 kHz becomes 40 kHz for 44.1 to 88.2.

Got it - thanks

For 705/768 WTA1 is in pass through mode, so it's not filtered. After WTA1 you have two choices - either WTA2 (which is a linear phase symmetrical WTA filter that takes you from 16FS (786 kHz) to 256 FS (12,288 kHz or 12.288 MHz) - the white and green filter - or an IIR filter. This 3 stage IIR filter either starts at 256FS (white or green) or takes over at 16FS to replace WTA2 (orange or red). The time constants for this filter is adjustable (about 240 kHz or 60 kHz) and this gives us the high frequency filter (white/orange off, green/red on). The intent on this filter is to remove the ADC distortion and noise that plagues HD recordings.

Is there any spec sheet that describes exactly what each of the four filters (white, green, orange, red) do in pass-through mode? It seems you're saying there's an infinite impulse response filter applied with all four settings (red, orange, green, white): "This 3 stage IIR filter either starts at 256FS (white or green) or takes over at 16FS to replace WTA2 (orange or red)." Is that right? If so, how does this filter distinguish between physical content of the recording and distortion/noise artifacts? I presume there's a risk this could filter out something it's not supposed to? The backdrop to all this is I'm wondering what the optimal connections/settings are on Qutest when being fed by the M Scaler.

 

[Rob Watts]

And just to be certain is using pin 2 and 3 the best way to connect to the speaker - I asked before but the person checking it out wants to be careful.

I use my TT2 for driving B and W 803D3 in single ended mode - that would be pin 1 (gnd) and pin 2 (hot) on the XLR.

Is there any spec sheet that describes exactly what each of the four filters (white, green, orange, red) do in pass-through mode? It seems you're saying there's an infinite impulse response filter applied with all four settings (red, orange, green, white): "This 3 stage IIR filter either starts at 256FS (white or green) or takes over at 16FS to replace WTA2 (orange or red)." Is that right? If so, how does this filter distinguish between physical content of the recording and distortion/noise artifacts? I presume there's a risk this could filter out something it's not supposed to? The backdrop to all this is I'm wondering what the optimal connections/settings are on Qutest when being fed by the M Scaler.

Yes there is always a third order low pass filter - this does the filtering to 2048 FS. It's equivalent to a RC type filter. By engaging the HF filter you change the time constants of these filters.

I never use orange/red - I just set it to green as some of my recordings are 96k; its 96/192k where the benefits of HF filter is really noticeable.

 

[csglinux]

I use my TT2 for driving B and W 803D3 in single ended mode - that would be pin 1 (gnd) and pin 2 (hot) on the XLR.



Yes there is always a third order low pass filter - this does the filtering to 2048 FS. It's equivalent to a RC type filter. By engaging the HF filter you change the time constants of these filters.

I never use orange/red - I just set it to green as some of my recordings are 96k; its 96/192k where the benefits of HF filter is really noticeable.

So when connecting M Scaler to Qutest, do you recommend white or green filter on Qutest, or does this simply depend on the source?

 

[Rob Watts]

M scaler doesn't matter to choice of filter, as it's only substituting WTA 1. So I use green (in fact I only listen with M scalers, I carry one on flights too).

 

[ZappaMan]

M scaler doesn't matter to choice of filter, as it's only substituting WTA 1. So I use green (in fact I only listen with M scalers, I carry one on flights too).

What is green on tt2 rob?

 

[Muataz]

MIT Research: Why Ears Have "Exquisite" Sensitivity
http://news.mit.edu/2019/mechanism-explains-ear-sensitivity-0116