Which DACs bypass digital filtering?

[bogi]

On 3/6/2022 at 2:26 PM, giordy60 said:

a question....
topping E30 should bypass internal circuitry when in dac mode ....
if I send a 16 / 44.1 file from HQP and set an upsampling to dsd 512 I see 22.57 mhz on the topping display and it is correct .....
if I send a 24/96 file from HQP always with upsampling to dsd 512 I should see 24.576 on the display ... and instead I always see 22.57mhz .....
  E30 topping does not handle 48K files?
E30 topping with obvious AKM chip .....
I tried both on NAA (windows) with driver topping and on naa with Miska image
thanks to those who can answer.

I know I am very late with this answer. If you still own it, maybe it will help. I owned E30 about 2 years ago - the 1st generation - I know they later changed things so not all E30 sounds the same. My answer is related to the oldest E30 and the 1st firmware.

a) DOP mode (DSD128 6.144 MHz, DSD256 12.288MHz)
48k based DSD content plays OK but E30 display shows 11.28 instead of 6.14 for DSD128 and 22.57 instead of 12.28 for DSD256. For DSD128 the Topping ASIO driver Control Panel shows 384000 Hz (that's the correct expected value for DoP DSD128).

b) native DSD (DSD128 6.144MHz, DSD256 12.288MHz, DSD512 24.576MHz)
If 44.1k based content (PCM or DSD) was played before, after switching to 48k based DSD sample rate (say DSD128 6.144) the E30 display shows 5.64 and music plays slower than it should in the ratio 44.1 / 48. The work around is to switch to DoP and back. Then the music content will be played without issues but the E30 display shows 11.28 instead of 6.14 for DSD128 and 22.57 instead of 12.28 for DSD256 (like in DoP). The ASIO driver control panel shows correct DSD sample rate (6144000 Hz for DSD128, 12288000for DSD256). If 48k based content was played before, switching to DoP and back is not needed to get correct playback speed.
DSD512 24.576MHz does not bring any sound from E30. HQPlayer is playing and sending data into the DAC, ASIO driver control panel shows correct sample rate 24576000 Hz and it seems the E30 XMOS receiver is getting data, but display incorrectly shows 45.15 and no sound is coming from analog outputs.
The 44.1k based DSD512 content plays without issues in native DSD mode.

I mentioned the issue also
here https://audiophilestyle.com/forums/topic/19715-hq-player/?do=findComment&comment=1085892

and here https://audiophilestyle.com/forums/topic/19715-hq-player/page/964/

 

[bogi]

3 hours ago, Yurii said:

All ESS chips use DSD to PCM conversion. And why do we need it?

No ESS chip does lossy downsampling to PCM rates. ESS chips send incoming DSD stream through IIR filter (volume processing is part of it), then through delta sigma modulator and finally through D/A conversion stage. It's not back converting to PCM rates but it also isn't direct DSD.

 

https://audiophilestyle.com/forums/topic/62699-a-toast-to-pggb-a-heady-brew-of-math-and-magic/?do=findComment&comment=1239324

On 4/17/2023 at 11:12 AM, Miska said:

DSD goes through the 3rd order IIR without any rate conversion and then goes through the modulator to the conversion.

[bogi]

1 hour ago, Miska said:

Gustard A26 is on my pending list, since it has some firmware bugs that should be fixed first.

Did you have an opportunity to measure it?

[bogi]

@Nkam That's about analog filter behind AKM DAC chip.

[bogi]

But I see it could be about digital DSD filter setting - from manual:

 

The menu is switched by the movement of the digital cursor, as follows:
—1). PCM digital filter adjustment
—2).DSD digital filter adjustment
—3).DSD direct mode decoding
—4 ). Clock source selection

 

AFAIK for example analog output of ESS chips needs yet to be additionally filtered in analog domain.

We understand direct DSD path as path where no lossy operation appears in digital domain.

So I am interested about more information about nature of DSD digital filters used.

If I well understand, it is about filters in AK4191 chip (not AK4499EX).

 

 

About direct DSD A26 manual says: "When this option is turned on ( EN A B L E ), it will pass through DSD , and only the most original DSD signal at the front end will be sent to the decoding circuit. "

But then what is the meaning of 'DSD Filter 2' on the picture? Miska, could you please explain?

[bogi]

29 minutes ago, Yurii said:

If you want to understand what is required to convert DSD to analog, then look at the photo.

 

I was discussing Gustard A26.

 

18 minutes ago, Yurii said:

The DSD path selects a DSDD value of 0 or 1 from the control processor. Direct DSD is value 1 and path through Filter2. Through Filter1, the signal is converted for digital volume control.

 

I was interested in 'DSD Filter 2'. You provided no information what couldn't be seen on the picture.

 

Your previous posts look similar. In 9 years you are the 2nd person I added to my ignore list so I will no more react on you. The first one @plissken was later permanently banned by Chris since he repeatedly disrupted threads.

[bogi]

28 minutes ago, semente said:

 

It looks like 'DSD Filter 1' goes through DSP and the SDM, and 'DSD Filter 2' has a direct path to the D/A stage.

 

DSD filter 1 and 2 (selection by menu item 2) is not  about switching paths to path 1 or path 2. That's done by menu item 3.

 

AK4191 datasheet states:

 

I am interested to discuss if DSD stream processing through such a FIR filter is or can be considered lossless. And if path containing such a FIR filter fits to how we understand the term 'direct DSD path'.

 

[bogi]

28 minutes ago, semente said:

Are they digital or analogue FIR filters?

 

Digital. The whole chip AK4191 is digital. D/A conversion is performed in AK4499EX. Data interface between those two chips is 5 to 7 bits binary weighted at ~ MHz sample rates (like also DSD rates are).

[bogi]

2 hours ago, davide256 said:

Gustard R26 claims it’s native DSD, + R2R NOS for PCM. Is it truly native DSD?

From R26 manual:

 

It contains two discrete DAC implementations in one case. l7audiolab measurements show high noise floor of DSD part. Wolf used Roon to upsample 48k/24b test signal to DSD256. I don't know if (how much) it could influence measurement results.

[bogi]

5 minutes ago, Nkam said:

well Roon will upsample PCM 48khz to DSD even if the DAC does not support it. 

I had test signal quality in my mind. It may impact measurement results. But I don't know how much.

One could generate higher resolution PCM test signal and then convert it to DSD in HQPlayer Pro.

[bogi]

@Miska could you please answer yet this post? https://audiophilestyle.com/forums/topic/31941-which-dacs-bypass-digital-filtering/page/23/#comment-1240758

[bogi]

1 hour ago, davide256 said:

Trying to follow this. Are you talking about up-sampling 44.1 PCM to DSD?

> Modulator choice has big impact on any SDM performance.
This was about creating DSD test signal from PCM test signal. There are no DSD test signals publicly available for download so one has to find a software tool and generate one. Miska told that software delta sigma modulator used in PCM to DSD conversion has big impact on conversion result.

> (and roon produces just multiples of 44.1k, AFAIK)

Not every PCM to DSD capable tool/program is able to generate 48k based DSD content. That explains that Wolf could not measure 48k based DSD with Roon (if he would want to).

 

> But R26 seems to have some bug where DSD at multiples of 44.1k produce noisy output, while DSD at multiples of 48k doesn't.

That's about Miska's R26 measurements with DSD input (Miska of course can generate 48k DSD test signal).

[bogi]

15 minutes ago, Miska said:

Essentially, the DWA section in 4499EX is also analog FIR.

 

I was pointing to AK4191 'DSD Filter 2', not to AK4499EX. AK4191 is digital circuit. Gustard menu contains "DSD digital filter adjustment". When DSDD bit is set to "1", there is no way to skip 'DSD Filter 2', which is digital FIR filter described as "FIR filter that reduces high frequency noise of DSD input data". 'DSD Filter 2' has clearly digital input and digital output.

 

 

This thread is named "Which DACs bypass digital filtering". My question remains. Can be DSD input stream processing through such a FIR filter considered lossless? Does DSD signal path containing such a FIR filter fit to our understanding of the term 'direct DSD path'? ESS DSD path also contains FIR filter, but followed by additional modulation before D/A stage. So there is my question what can be yet considered to be direct DSD path and why.

 

I could understand your word "essentially" this way:

'DSD filter 1' is digital filter, but it is essentially used for the same thing like analog one. DSD signal needs nothing more than low pass filtering to get analog signal. Low pass filtering can be done in both digital and analog domains. If we do some preliminary low pass filtering (removing of high frequency content) in digital domain and then follow it with analog filtering, in principle it brings the same type of ananlog result as pure analog filtering. Did I understand your "essentially" well?
 

[bogi]

50 minutes ago, Miska said:

No, because you have the modulator in the path. So you are not converting the original data to analog.

 

I'm sorry I intended to write 'DSD Filter 2' not 1 in my previous post. I did not mean the path with volume control and modulator in it.

 

55 minutes ago, Miska said:

Here, you can conclude that the Filter 2 essentially rearranges the data to match input requirements of the 4499EX.

 

That's helpful explanation. Is the "internal DSD filter cut off frequency" result of data re-arrangement (to binary weighted 5 to 7 bit with possible rate lowering to fit the rate between chips) or do you expect any additional data processing algorithm yet to be used to filter high frequency noise, as suggested by "reduces high frequency noise in DSD input data" from the datasheet?

[bogi]

6 minutes ago, Miska said:

Data arrangement in 4191 combined with the 4499EX operation forms the desired filter characteristics. Similar way as in TI/BB chips it gives the four analog FIR response options depending on how the data is arranged.

 

Thanks. That's much more understandable than the datasheet formulation.

[bogi]

49 minutes ago, davide256 said:

What does 1 bit multi-megabit encoded DSD recordings have to do with N x CD rate? I see the 48K option on HQPlayer output choices but have never really understood why its there.

 

DSD is 1 bit signal at high rates. Something like very very quickly blinking LED lamp, where average density of '1' (light on) defines the light intensity in a time interval the density is related to. If LED lamp operates on very high frequencies so we cannot distinguish individual blinks, our eyes do such an averaging. In fact our eyes do low pass filtering with high frequency light content, similar like delta sigma DACs do with upsampled and delta sigma modulated audio content.

 

DSD signal bit rate can be of different values. Usual values are multiples of 44.1k base. For example DSD64 rate (used for SACD) is 64 x 44.1k = 2.8224M. That's what DAC may display as incoming sample rate. DSD512 is at 512 x 44.1k rate. High resoultion DSD downloads in DSF format are by a convention at 44.1k based rates (44.1k x N, N is usually 64, 128 or 256).

 

But then there are people like we who are doing PCM to DSD upsampling in HQPlayer or any other player capable of that. Many of us apply PCM to DSD conversion for every PCM content, not only for 44.1k based one. For N x 48k based PCM content we may configure HQPlayer if we want it to output for example DSD256 at 256 x 44.1k rate or at 48k x 256 rate. Why at all to use those 48k based rates for DSD? For me, from two reasons:

1) Integer upsampling ratio (like 48k -> 48 x 256) is less CPU demanding than when the ratio is non integer (like 48 -> 44.1 x 256 ). With non integer ratios you easier get dropouts because of insufficient CPU power.

2) 48 x 256 is more than 44.1 x 256. It may sound a bit better. From the same reason why DSD512 may sound better than DSD256. Of course, these things depend on concrete DAC implementation so it need not be a general rule.

 

Not all DACs support 48k based DSD rates. If that support is missing, it may be harder to upsample 48k based PCM content to DSD than 44.1k based content - because of that non integer ratio. People owning such a DAC may prefer 44.1k based PCM content over 48k based one because it may be easier playable in HQPlayer when PCM to DSD conversion is used.

[bogi]

11 hours ago, Nkam said:

what are this guy ‘ Wolfs’ credentials anyway?

AFAIK he is a Chinese professor, respected in their hifi community. I don't know his real name.

[bogi]

8 hours ago, Nkam said:

so basically we know nothing

Nothing personal. But he owns an expensive AP measurement unit and he knows how to use it. His comments under his series of measurements show he understands the devices. He found some bugs in tested devices and communicated them with manufacturers. He has contacts to manufacturers in that region and sometimes he tests pre-production pieces.

[bogi]

26 minutes ago, Nkam said:

nothing personal as well brother.  We all look at things through a different lens

I have no problem with your opinion. Just few points: Posting about device bugs or poor performance in some areas does not look as promotion. His conclusions about Gustard R26 are far from "this is a perfect device, buy it".

 

There are also some regional differences between for example U.S. and Asian countries. Then, there are people even from "western" world who as part of their hobby do things for free. You can for example explain me @Archimago's  commercial intentions.

 

In the past I did reviews of headphone rigs in Slovak. People from Slovak and Czech hifi forums sent me devices sometimes costing more than $1000 without knowing me in person. I am an I.T. person and I have no audio related commercial interests.

 

But we are going to be too off topic, IMO better to stop here.

[bogi]

15 hours ago, taipan254 said:

didn't see the E70 Velvet from Topping in here

I read the positive-feedback article about E70 velvet but I also read from other sources. I did not find any really serious confirmation that E70 velvet does direct DSD (in the sense of skipping delta sigma modulator). The positive feedback article is written by person with no previous experiences with direct DSD and shows low level of DSD topic related knowledge, so it is not enough trustworthy for me.

[bogi]

1 hour ago, semente said:

Topping E30, T70, T90 (AKM)

 

Correction: D70, D90.

[bogi]

@semente yet look at my above post :)

[bogi]

3 hours ago, GregHouse said:

Can a DAC that is not PCM true NOS become PCM true NOS only with a firmware update, or is it a hardware issue?

 

Real NOS is impossible for example with delta sigma architecture DAC chips. Such a DAC chip will always oversamle up to delta sigma modulator operating frequency, which appears somewhere in MHz range. Firmware update couldn't change the fact that internal oversampling and delta sigma modulator cannot be skipped with PCM input.

[bogi]

Audalytic AH90 (Gustard brand) direct DSD works the same as for A26 (firmware update is available)
It is a cheaper variant of A26 (so it also includes LAN input and computer part) with added headamp.

According to iiWi Reviews it has brighter sound signature more similar to some Sabre implementations, lacking body and weight in comparison to for example SMSL D400 EX with the same AKM chipset.

[bogi]

15 minutes ago, Miska said:

But it most likely wasn't tested in DSD Direct mode... Which most likely doesn't work on SMSL D400 EX (since it doesn't work on two other SMSL models using same chipset).

Right, D400EX is mentioned in iiWi Reviews only in context of sound signature comparison with Audalytic AH90 and it was based on PCM content as usual. I had no intention to mention D400 EX in relation to direct DSD - that's most probably not available.