Modern Multi-Bit DAC vs Delta Sigma, specifically AKM's newest flagship, but also others

[solderdude]

The L70 (headphone amp twin of the E70/E70 Velvet, which I also have) has one of these internal resistor ladder networks I think. I believe I saw a picture of about 25 resistors for all 200 positions between 0.0dB and -99.5dB

This is just for volume control and linearity (resistor tolerance) is not an issue here, in DACs it is as they are switched constantly.

The more resistors (and relays or SS switches) the smaller the steps can be. Once the volume is adjusted there is no switching.

 

[Killingbeans]

Put even more simply: it's a 7 bit multi-bit DAC running at a higher frequency which essentially allows it to resolve more bits. Correct?

Yes. But the same thing can be said about the 1 bit DAC in the most simple version of an SD DAC.

It's a compromise. Pushing the performance of an SD DAC further by paralleling weighted outputs, but keeping the amount of bits low enough to avoid having the DA stage negate that performance gain.

Are they because the more resistors you have, the more exact their tolerance must be?

Yes, and higher production cost, lower yields, more area to pick up noise etc. etc.

 

[mike7877]

Yep.

A lot of DS DACs usually are 5 to 6 bit. It really is not such a big deal.
The biggest challenge is to get the maximum speed higher so DS can be at a higher switching speed. One runs into practical limits.

There is nothing really 'special' about 7 bits DS.

This really makes me mad. I'm not mad because the E70 Velvet sounds great, but I'm mad at the deception. If it's not a premium switched resistor stereo DAC, don't call it a switched resistor stereo DAC, call it a DS DAC with an extra bit or two...

 

[DonH56]

There are many ways to implement conventional and delta-sigma DACs. Most if not all modern delta-sigma DACs have multi-bit internal DAC stages to improve resolution without requiring much higher sampling rates. Here are a couple of basic DAC articles on ASR:

Digital Audio Converters (DACs) Fundamentals

Author: our resident expert, DonH50 The purpose of this thread is to provide a quick introduction to digital-to-analog converters (DACs), the magical things that turn digital bits into analog sound. Previous threads have discussed sampling theory, aliasing, and jitter. Now we’ll get down to the...

www.audiosciencereview.com

Delta-Sigma Digital Audio Converters (DAC)

Note: this article was originally written by our DAC/technical expert, @DonH56. The previous thread on DAC fundamentals provided an overview of conventional (Nyquist) DACs. This thread will introduce oversampling and the delta-sigma architecture that dominates the DACs used in consumer audio...

www.audiosciencereview.com

A conventional multibit DAC uses resistors or current sources and is segmented to reduce the number of cells inside the DAC. An N-bit DAC requires 2^N cells; segmenting allows far fewer cells to be used. There is an art and science involved to choose the final architecture and it is usually application-dependent.

Edit: The delta-sigma article was supposed to have another section on multibit DACs, but that part was lost. I added a brief paragraph to the thread; Amir posted the article for me when he ported a bunch of early articles so I cannot edit it myself.

 

[solderdude]

This really makes me mad. I'm not mad because the E70 Velvet sounds great, but I'm mad at the deception. If it's not a premium switched resistor stereo DAC, don't call it a switched resistor stereo DAC, call it a DS DAC with an extra bit or two...

They did not lie here. The DAC section is a switched resistor stereo DAC. But just 7 bits and at a very high speed (DS).
Just like any other DS DAC (or switched current sources)

 

[JustJones]

The 4191 is 64 bit the 4493s is 32 bit.

Audio D/A Converters | Audio Components | Products | Asahi Kasei Microdevices (AKM)

AKM’s audio D/A converters (DACs) provide solutions for high quality audio system with the original digital-analog mixing technology.

www.akm.com

 

[voodooless]

I'm mad at the deception. If it's not a premium switched resistor stereo DAC, don't call it a switched resistor stereo DAC, call it a DS DAC with an extra bit or two...

There is no deception. It is what it says on the tin. No, it’s not a ladder R2R DAC, nor is this claimed anywhere.

 

[mike7877]

Pushing the performance of an SD DAC further by paralleling weighted outputs

By this do you mean using the outputs from both channels of a stereo DAC for the same channel like is commonly done?

 

[mike7877]

The 4191 is 64 bit the 4493s is 32 bit.

Audio D/A Converters | Audio Components | Products | Asahi Kasei Microdevices (AKM)

AKM’s audio D/A converters (DACs) provide solutions for high quality audio system with the original digital-analog mixing technology.

www.akm.com

The 4191 does 64 bit processing internally, and the 4493s accepts 32 bit signals, but we're talking about the D/A conversion stage in the chip, specifically

 

[Killingbeans]

This really makes me mad. I'm not mad because the E70 Velvet sounds great, but I'm mad at the deception. If it's not a premium switched resistor stereo DAC, don't call it a switched resistor stereo DAC, call it a DS DAC with an extra bit or two...

Don't be mad at AKM. Be mad at the audiophile world for taking the term "multi-bit" as hostage.

From a technical point of view it doesn't make much sense when audio entusiast talk about "multi-bit DACs"

 

[voodooless]

The 4191 does 64 bit processing internally, and the 4493s accepts 32 bit signals, but we're talking about the D/A conversion stage in the chip, specifically

The 4191 does not do any D/A conversion.. it is not a DAC.

 

[mike7877]

There is no deception. It is what it says on the tin. No, it’s not a ladder R2R DAC, nor is this claimed anywhere.

I didn't say it was a ladder, ladder type was only mentioned briefly in another post as another option for the resistor network for a multi-bit DAC.

"The AK4499EX is a new concept Premium multi-bit Stereo DAC with newly developed Switched Resistor technology"

I'm disappointed because it's just a SD/DS DAC, not like the quote from the top of the 100 page datasheet for the 4499EXEQ (Velvet)

 

[Killingbeans]

By this do you mean using the outputs from both channels of a stereo DAC for the same channel like is commonly done?

No. I mean by using multi-bit quantizers and feeding their outputs to a multi-bit DAC internally.

 

[voodooless]

I didn't say it was a ladder, ladder type was only mentioned briefly in another post as another option for the resistor network for a multi-bit DAC.

"The AK4499EX is a new concept Premium multi-bit Stereo DAC with newly developed Switched Resistor technology"

I'm disappointed because it's just a SD/DS DAC, not like the quote from the top of the 100 page datasheet for the 4499EXEQ (Velvet)

Because it’s not a DS DAC! The DS modulation is done outside of the chip. You can also use it a a conventional 7-bit R2R DAC if you like…

 

[mike7877]

They did not lie here. The DAC section is a switched resistor stereo DAC. But just 7 bits and at a very high speed (DS).
Just like any other DS DAC (or switched current sources)

But this isn't the datasheet:

All of their other DACs are Sigma-Delta, and this one is a "Premium Switched Resistor"

The way they include 7 bit, to the less informed, seems to imply the data interface is 7 bits wide.


They didn't put 24 bit on the front page because if it's a "premium switched resistor DAC", it's not 24 bit.
To be able to call it a switched resistor DAC, and not a sigma delta DAC, they cannot advertise it being 24 bit.
It can be a 24 bit sigma delta, and a 7 bit switched resistor running in turbo mode (lol)

IMHO, they could have been more forthcoming. This is their flagship... nothing is accidental here

 

[mike7877]

The 4191 does not do any D/A conversion.. it is not a DAC.

I didn't say it did. I said it did internal processing...
like discussed earlier in this thread.

 

[mike7877]

Because it’s not a DS DAC! The DS modulation is done outside of the chip. You can also use it a a conventional 7-bit R2R DAC if you like…

Do you have any examples of it being used like that? (as a 7-bit R2R DAC)

You seem... confrontational. Did I do something wrong?

 

[DonH56]

But this isn't the datasheet:
View attachment 352996

All of their other DACs are Sigma-Delta, and this one is a "Premium Switched Resistor"

The way they include 7 bit, to the less informed, seems to imply the data interface is 7 bits wide.


They didn't put 24 bit on the front page because if it's a "premium switched resistor DAC", it's not 24 bit.
To be able to call it a switched resistor DAC, and not a sigma delta DAC, they cannot advertise it being 24 bit.
It can be a 24 bit sigma delta, and a 7 bit switched resistor running in turbo mode (lol)

IMHO, they could have been more forthcoming. This is their flagship... nothing is accidental here

No, it is a 7-bit modulator, so the internal DAC is 7 bits and is used in a delta-sigma loop. The loop oversamples the 7-bit data, modulates it using a delta-sigma loop to push the noise above the audio band, then applies a filter to prevent the excess high-frequency noise from appearing at the output. The end result is a DAC exhibiting roughly 23-bit performance. That is how a delta-sigma design works; please check the link I provided earlier.

I doubt it is a simple R2R DAC, I would expect the MSBs to be segmented into unary (unit) cells with R2R used for the lower bits -- that is how most "R2R" DACs actually work. A unary 7-bit DAC would have 127 cells, possible in an IC, and greatly reduces the need for trimming and such.

 

[mike7877]

No, it is a 7-bit modulator, so the internal DAC is 7 bits and is used in a delta-sigma loop. The loop oversamples the 7-bit data, modulates it using a delta-sigma loop to push the noise above the audio band, then applies a filter to prevent the excess high-frequency noise from appearing at the output. The end result is a DAC exhibiting roughly 23-bit performance. That is how a delta-sigma design works; please check the link I provided earlier.

Ah, I understand a bit more now

But the point I'm trying to make is that this is advertised, not as a delta-sigma, but "premium switched resistor" DAC (title on datasheet).
It's not used as a 7 bit switched resistor DAC, and (IMO) if we're talking audio, 7 bit isn't premium

 

[voodooless]

Do you have any examples of it being used like that? (as a 7-bit R2R DAC)

Well, it’s a switched resistor DAC, which is not exactly the same as R2R, but it’s close enough.

You seem... confrontational. Did I do something wrong?

I’m just pointing you towards the correct answers