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DAC attenuation before power amp

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#1
With dedicated DACs becoming so cheap, and computer-consumed media becoming so common, single source systems are starting to become more popular, maybe removing the need for large parts of what pre-amps typically offered to end users, namly source selection and integrated phono pre-amps.

One thing that is still needed between your source and power amplifier though is an attenuator of some sort. Assuming a "standard" setup of 16-bit playback that outputs 2 volts, it seems like there are a two options, attenuate the playback signal, outputting less than 16 bits and losing resolution, and outputting less than 2 volts.

1. Attenuate before the dac. In the case of PC playback, this means the digital volume there. This has the benefits of being able to easily control remotely (from your phone, for example), but should have the effect of reducing resolution (less available bits). Is this at all a feasible choice given alternatives? Are there playback stacks that allow attenuating here while still maintaining resolution?

2. Digital volume control on the dac. Topping D50 stands out as an option here. This seems like it will "just" attenuate the output signal, so no loss of resolution, and in addition is digital so perfect channel tracking. Downsides is this limits DAC choice to somewhat more expensive options. DX7 allows remote control here, which is a worthy consideration, but again increases price somewhat.

3. Passive attenuator in between DAC and downstream. Something like the Mackie BigKnob, schiit sys, various nobsound products. Essentially attenuator in a box, with 2 rca inputs, 2 rca outputs, and a knob to control output. These should reduce output, but will impedance matching become a problem here? In some worlds you can even locate this box near the listening position to allow ease of adjustment (especially if you can get XLR to help with noise rejection on the longer runs).

4. "Real" preamps. This includes stuff like AV receivers with pre-outs, emotiva pt-100, exotic things, etc.

5. Other pro audio things that I'm missing? The passive knobs tend to be in the pro audio realm, maybe there's some other choices here?

The idea of option 3 is appealing to me, and is largely the reason why I'm typing this, because something like Topping D10 + a knob of some sort comes out to <$200, and probably <$150 and seems very appealing to front a signal chain that either goes directly to an amp next, or goes to some sort of other signal processing next (minidsp etc for sub crossover, for example), maintaining flexibility while still having great options to choose various components. It also allows me to easily add a splitter of some sort in order to get output to headphones as appropriate.

Are the potential impedance problems with a passive volume control really a problem with well designed amp and dac? Am I better off just grabbing either a D50/DX7 or some emotiva type product as the "front" of my system? Are there other options/science to consideR?
 

Ron Texas

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#2
The Topping D30 follows the volume control in Windows. It's not the only DAC which does that. I run it straight into a Crown XLS 1502.
 
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#3
Right but when controlling signal output "before" the dac, isn't that basically trimming off bits of resolution, ultimately lowering things like SNR?
 

andreasmaaan

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#4
Right but when controlling signal output "before" the dac, isn't that basically trimming off bits of resolution, ultimately lowering things like SNR?
Depends how it’s done actually. Better software will process the data at 32 bits and attenuate losslessly if the input is a 16 bit file.
 

Blumlein 88

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#5
This below is an excerpt from the jriver wiki about volume control in their media center.

The precision offered by Media Center's 64bit audio engine is billions of times greater than the best hardware can utilize. In other words, it is bit-perfect on all known hardware.

To demonstrate the incredible precision of 64bit audio, imagine applying 100 million random volume changes (huge changes from -100 to 100 dB), and then applying those same 100 million volume changes again in the opposite direction.


Amazingly, you will have the exact same signal at 32bit after 200 million huge volume changes as when you started.

In other words, this incredible number of changes results in a bit-perfect output at 32bit, which is the highest hardware output bitdepth (most high-end hardware is 24bit).

This also means one volume change or a series of 100 million volume changes that add up to the same net result is bit-identical.

So any software doing 64 bit volume control is going to be effectively beyond reproach. It will be beyond the precision in any mechanical/electrical volume control anyone could possibly manage to build. Now one could end up using a DAC at such a low level the linearity will become a problem perhaps. Even that is unlikely with the sigma delta DACs of quality. Plus electromechanical volume controls have various linearity issues of their own.

Almost any DAC will be 24 bit in how it handles the data. Some are even 32 bit now. Software for playback is usually 32 bit float or 64 bit. The result of lowering the signal is going to be a 24 bit output which isn't really lowering resolution. You loose resolution to noise even with an analog volume control. The current good playback software volume controls are going to create less negative effects than mechanical attenuation.
 
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#6
So then option 1 becomes the best choice here? Get a reasonable dac (D10, whatever), feed it via a good playback mechanism that can run > 16 bits, and then I get good/perfect digital volume control with seemingly no compromises?
 

andreasmaaan

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#7
So then option 1 becomes the best choice here? Get a reasonable dac (D10, whatever), feed it via a good playback mechanism that can run > 32 bits, and then I get good/perfect digital volume control with seemingly no compromises?
Absolutely :)
 

Ron Texas

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#9
Right but when controlling signal output "before" the dac, isn't that basically trimming off bits of resolution, ultimately lowering things like SNR?
What's happening is the D30 is using its internal volume control reading the Windows volume control for advice. I suppose that I could set up the D30 as being other than the default audio device with it's volume at 100% and use the software control in foobar, JRiver or whatever.
 

RayDunzl

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#10
Digital Attenuation example, using 24 bits:

1545695338673.png


Hint: -60dB is a lot of attenuation
 

Blumlein 88

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#11
What's happening is the D30 is using its internal volume control reading the Windows volume control for advice. I suppose that I could set up the D30 as being other than the default audio device with it's volume at 100% and use the software control in foobar, JRiver or whatever.
Yes you could do that. The DATA sheet for the Cirrus DAC says it has non-decimating volume control in 1/2 db step sizes. So it may be doing no harm anyway. But I don't know the full details of what they are doing in the chip itself.
 

Ron Texas

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#12
Yes you could do that. The DATA sheet for the Cirrus DAC says it has non-decimating volume control in 1/2 db step sizes. So it may be doing no harm anyway. But I don't know the full details of what they are doing in the chip itself.
Since reading this I have set the Realtek motherboard audio as default and windows volume for the D30 at 100, using the playback program for volume control. It might sound better or it might not. I hesitate to make claims, but anyone with a D30 can try it themselves for free.
 

bennetng

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#13
The advantage of floating point processing is the ability to maintain constant precision over a very wide volume range and eliminate the risk of clipping during internal processing. I posted a calculator here:
https://www.audiosciencereview.com/...lity-in-windows-using-wasapi.5272/post-117437

As you can see, my calculator showed slightly different values than ESS' result after rounding (9487.7817 vs 9487.7813) even though both examples are 32-bit, Why?

ESS' implementation (as well as other manufacturers) is not really working in floating point, it is just fixed point with padding. In their second example they used -35dB and resulted in 533.5372. In my calculator if you do the same the result will be 533.53717.

To make the difference more obvious, let's reduce much more. For integer systems, one bit has about 6.0206dB of dynamic range, so the limit of 32-bit fixed point is about 192.6592dB. Let's set the integer bit depth to 32-bit and calculate the value of -167dBFS. It shows 9.592457099740953 in 64-bit float. Click "Convert to single" to show 9.5924568 in 32-bit float. Click "Convert to fixed" to discard all values beyond the decimal point and get 10. In this case 32-bit float is able to maintain about 7 digits of precision while 32-bit fixed is much less accurate. Sure, -167dBFS is complete nonsense in practical usage but it is just a demonstration of how floating point works.
167.png



On the other hand, if you enter any >= 0 values in the "dBFS to sample" field, for example 2.7dBFS in Figure 4.40 of this tutorial:
http://www.adobepress.com/articles/article.asp?p=2171314&seqNum=7


44714.png


In floating point domain all illegal values are preserved, but once you click "Convert to fixed", everything will be clipped. It is exactly what happens if you don't decrease volume before audio data leave the playback software, or if you convert any floating point formats with positive peak values to integer formats like FLAC. It is also interesting that Audition shows "possibly" clipped samples. Why "possibly"? For floating point data, it is able to detect absolute clipping after fixed-point conversion since it can store normalized values beyond -32768 or +32767, but for fixed point data like FLAC import, it can only guess clipping by finding values which are exactly -32768 or +32767.

Digital volume control on DAC is not particularly useful due to the inability to handle floating point induced clipping, just use the floating point capable internal volume control on playback software, and optionally analog volume control on preamp or speakers for safety and convenience. A simple DAC with fixed output is perfectly fine.
 
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#14
I was also interested in this subject because I intended to go from dac into power amp so I experimented a little with digital volume control.
I tested a year ago my Sabre9018 based dac and at -35db the sound was... off. Especially the voices felt disconnected, the bass wasn't right also... the sound was just bad!
I tested recently my new dac (D50) and somewhere ~ -40db it is still something wrong. It's not nearly as bad as my previous 9018 but I still don't like my music. It is a bit disappointing since I had high hopes about digital volume.
All tests have been done with 24192 PCM.

I think smart software attenuation could be an option (I liked HQPlayer's volume control) but I can't find any player that sounds good in Windows. For that reason I'm using a minimalist Linux player. However when I will have the time I intend to try other players searching for a good one with a good volume control.

I wonder if could be possible for dacs to have some sort of attenuators in the analog section. Maybe something very simple like jumpers that control resistors... don't know.. -10db, -20db, -30db. With another 30db from the digital section probably enough for some/most people.
 

Blumlein 88

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#15
I was also interested in this subject because I intended to go from dac into power amp so I experimented a little with digital volume control.
I tested a year ago my Sabre9018 based dac and at -35db the sound was... off. Especially the voices felt disconnected, the bass wasn't right also... the sound was just bad!
I tested recently my new dac (D50) and somewhere ~ -40db it is still something wrong. It's not nearly as bad as my previous 9018 but I still don't like my music. It is a bit disappointing since I had high hopes about digital volume.
All tests have been done with 24192 PCM.

I think smart software attenuation could be an option (I liked HQPlayer's volume control) but I can't find any player that sounds good in Windows. For that reason I'm using a minimalist Linux player. However when I will have the time I intend to try other players searching for a good one with a good volume control.

I wonder if could be possible for dacs to have some sort of attenuators in the analog section. Maybe something very simple like jumpers that control resistors... don't know.. -10db, -20db, -30db. With another 30db from the digital section probably enough for some/most people.
I'm not sure why you'd have problem with good software attenuation.

In any case, yes you could have switchable or jumpable resistor networks for various levels of attenuation. It just isn't common in many DACs. You could make such a box yourself with resistors in it.

You also could use an inline attenuator like this. Though I don't know the details of which impedance they are made to work best. They are best used near the amp input.
https://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0
1547079584003.png

Or these which are similar.
http://www.rothwellaudioproducts.co.uk/html/attenuators.html

1547079791774.png
 

restorer-john

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#16
With dedicated DACs becoming so cheap, and computer-consumed media becoming so common, single source systems are starting to become more popular, maybe removing the need for large parts of what pre-amps typically offered to end users, namly source selection and integrated phono pre-amps.
Traditional upper range preamplifiers have offered switchable direct source to volume/output buffer facilities for at least 30 years. Many preamplifiers even switched off the phono RIAA stages and other active stages when in 'direct' mode.

The lack of a traditional volume control is hardly a benefit in my opinion, as is a device bereft of additional inputs.
 
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#17
In my experience you get what you pay for. The less expensive in line attenuators and inexpensive passives like the Sys are not as transparent and dynamic as a Saga, for example. And using the Saga in active tube buffer mode can sound better than passive mode depending on the input impedance of your source and amp and the quality of the tube used.
 

solderdude

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#18
LDR attenuation is what you need !
 

Willem

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#20
I do indeed think the classic analogue pre amplifier has had its day, unless you still want to use analogue sources (I don´t). I have just disconnected my last one (a Quad 33).
In my home office I use only one source, my desktop computer streaming into an ODAC usb DAC and that into a refurbished Quad 405-2 power amp driving a pair of Harbeth P3ESRs. I started with digital volume control on the computer, and sonically that is indeed perfect for the reasons that were indicated, but there is a snag: inadvertently high volume that can blow up your expensive speakers. Also, I did not find it very convenient compared to a big knob. So I added an Emotiva Control Freak volume control in between the DAC and the power amplifier. This works fine. Emotiva have discontinued this unit, but there are other offerings. In my particular case there was an additional level mismatch between the ODAC's modern 2 Volt output level and the Quad's traditionally much higher input sensitivity at 0.5 Volt. Again, this allowed unexpectedly high volume levels, and forced me to use the Control Freak near its maximum attenuation level where such units are least accurate, so I added a pair of 12 dB inline attenuators. Levels are now well under control and sound quality is fine.
My bedroom system uses an Ava Maestro 50 chip amp with optical input and a Chromecast Audio as its only source. This little amp has a volume control, but it also has an auto on/off feature, so I can hide the unit. I use the amp's volume control to set a maximum level and the Chromecast Audio's volume control for further reduction.
The main system was modernized yesterday (Quad 606-2 power amp and Quad 2805 electrostats with B&W PV1d subwoofer equalized by an Antimode 8033 dsp room eq). I replaced the Quad 33 pre amplifier that I had used with a variety of analogue and increasingly only digital sources with their own built in DACs (Chromecast Audio, Bluray disc player and Panasonic Plasma tv) with a Pioneer U-05 DAC with a wide range of digital inputs and variable output. Using the digital ouputs of these three sources it works a treat: sound quality seems a bit better than before, and the Pioneer is also convenient to use (it has a remote control.... ). Thus far, the DAC's volume control seems cable of coping with the level mismatch between the DAC and the Quad power amplifier, but I can always experiment with some inline attenuators. Such DACs with multiple inputs and volume control really are the pre amplifiers of today. The only thing they are missing is tone and balance controls. For low bass, this is dealt with by the dsp room equalization of the subwoofer by my Antimode 8033 (highly recommended) and for the Chromecast I could additionally use its own tone control (a quite recent new feature). My Pioneer no longer offers any analogue inputs, but I am fine with that. The Chromecast Audio offers far better sound quality than my Linn Sondek LP12 vinyl deck, and internet radio, even at moderate bit rates, sounds better than FM radio.
 
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