Differences in sound: DAC vs. DAC + Pre-amplifier

[audiobomber]

1 hour ago, motberg said:

What do you guys think about adding sub-woofers in a DAC direct to amp system?

Is it OK to split a 2V RCA output and run a set of cables 1 meter to the amp, and another set to the subs maybe 4 meters each?

 

I get the feeling that most DAC makers generally are expecting the user to use a single set of outputs to a single receiving device.

 

That depends mostly on the DAC output capability and the load it will need to drive, i.e. the input impedance of the power amp and sub crossover. 

 

Initially I tried the above and was not satisfied. The sound was transparent and more detailed but music became boring (poor PRaT). I subsequently learned that the sub crossover I use has an input impedance of 6kΩ, and my power amps are 20kΩ. That's a combined load of 4.6kOhms. My DAC has very low input impedance, just a few ohms, but it could not provide sufficient current for this load. 

 

I found a solution though. I am running my monoblock power amps from the RCA outputs on my DAC/Pre. The DAC's XLR outputs are feeding a passive preamp with 50kΩ input impedance. The passive pre drives the sub crossover via RCA's. Combined load on the DAC is now 14kΩ. I am getting the best sound I've ever had.

 

Brand new, my analog preamp cost three times as much as my DAC/Pre. Nevertheless, I prefer the sound directly from DAC to amps. I ripped all my LP's and sold the preamp. 

 

One other more minor caveat. When I used an RCA splitter in a previous bi-amped system. I could always hear a slight deterioration due to the (high quality) splitter and ended up not using it.

[audiobomber]

47 minutes ago, barrows said:

I run a sub, but I always prefer to connect sub(s) to the amplifier output via a high level input rather than other connection schemes.

I did that for a while and it sounded decent, but not great. I am now running my subs through a miniDSP 2x4, which allows me to implement a more versatile crossover and DSP with auto filters via REW.

 

DSP filters and corrections brought the sound to a level not achievable with a traditional subwoofer crossover and amp. I am not aware of any way to implement DSP using high level sub inputs.

[audiobomber]

1 minute ago, DuckToller said:

Bonjour, Audiobomber.
Short question about miniDSP, do I assume correctly, that the signal for your Subs and your speakers will run through ADC-DAC conversion at 24/96 during the DSP? Please feel free to correct me about my assumption
I do have a 2x4miniDSP somewhere in the closet and may start testing during the confinement  period...
Cheers, DT

I do not run my monitors through the miniDSP, they run full range. The monitors are sealed, with a Q of 0.7 and roll off naturally, second-order Butterworth. The subs roll in at  80HzBW2, with Auto EQ and room correction via REW. 

PS My miniDSP 2x4 is the base model, ADC-DAC conversion at 24/48.

[audiobomber]

18 hours ago, Abtr said:

Now, apart from expensive pro-audio active crossovers there are not many commercial options for a simple, good quality active crossover for sub(s) and front speakers, operating at a given crossover frequency. MiniDSP is a very versatile solution which I may try but I don't particularly like the idea of an extra AD/DA conversion and I understand overall sound quality is not to write home about, which may largely be a problem of the analog output stage and/or the power supply.

There are miniDSP solutions that don't require an ADC. The SHD has one analog and several digital inputs and contains two DAC's, as well as digital coax outputs in case you want to use an outboard DAC (or two). The analog output stage was designed for miniDSP by a well-known DIYAudio member and is supposedly quite good. The minDSP SHD Studio is D-to-D only, no AD or DA converters. They have recently added a new model with inboard power amp.

 

The above come with a built-in streamer and Dirac license. 

https://www.minidsp.com/products/shd-series

[audiobomber]

I thought each -6dB level change dropped one bit. That would mean that a 24-bit DAC should be able to play at -48dB and still fully resolve 16 bits. Is it not that straightforward?

[audiobomber]

9 minutes ago, opus101 said:

If the 24-bit DAC's a perfect one that would be the case. But perfect 24-bit DACs don't exist - none that I'm aware of have a low enough noise floor to fully resolve 16 bits at 48dB attenuation.

I agree that a current state of the art DAC, anything below 21 bits is just noise. I assume though that first three bits being dropped in a 24-bit DAC are the noise, and the DAC can still resolve 21 bits cleanly. Never mind that most DAC's are at least 32 bits and have that much more bits to shed without truncating data.

 

Anyway, I don't think noise is a problem with virtually any modern DAC. I believe timing is a more important differentiation.

[audiobomber]

1 minute ago, opus101 said:

The fact that most DACs are 32-bit is more marketing than engineering.

Not if you're the DAC for digital level control. You need those extra bits to prevent data loss at lower levels. I typically run my 32-bit DAC between -27 to -9 dB. 

[audiobomber]

Just now, opus101 said:

I'm not following why you'd need no 'data loss' when the noise is above the signal level?

You said a 32-bit DAC is just marketing. Clearly I need a 32 bit DAC to run at -27dB, because if I had a 24-bit DAC, I would be dropping bits above the noise floor, i.e. data bits.

[audiobomber]

13 minutes ago, barrows said:

Guys, nobody achieves 21 bits of resolution in room, so there is no advantage to a DAC which achieves 21 bits of resolution at its analog outputs vs 20 bits, or even 18 bits.  When a DAC gets beyond 17-18 bits of resolution it is a moot point for listening to speaker systems in a  room.  If one is willing to risk their hearing in a headphone set up at extremely high levels of playback, then maybe 19 bits is meaningful, but for speaker systems these high levels of resolution mean nothing in the real world.

I agree with all that. All I'm saying is that you need at least a 32-bit DAC if you are using the DAC as a preamp. A 24 bit DAC is insufficient.

[audiobomber]

3 hours ago, Abtr said:

Here's what RME states about the digital volume control of their ADI-2 DAC:

 

 

The ADI-2 DAC deliberately avoids an analog level adjustment by means of a potentiometer. Its digital version surpasses an analog one in practically every conceivable point. Typical disadvantages of setting with potentiometers:

• Synchronicity errors lead to panoramic shifts and significant volume deviations left / right, in particular near the end points of the adjustment range.

• In the middle setting range, there is an increased crosstalk and changes in the frequency response. Changes in the frequency response also occur at the end regions of the adjustment path.

• The setting range for optimum volume adjustment is often too small, or at the lower or upper end of the potentiometer's adjustment range.

• Non-reproducible settings (except 0 and 11).

• Higher THD/THD+N. A point well known to measurement technicians. As soon as an analog potentiometer is in the signal path, the unstable contact between wiper and resistive track causes noise, which contains both THD (distortion) and N (noise), even in the stationary state. Thus the -110 dB of a DAC quickly gets reduced to for example -80 or -70 dB.

Special volume ICs, which activate different resistance values by means of numerous electronic switches, avoid some of the above mentioned points. Unfortunately, even the best of these ICs do not achieve either THD or dynamics of the DACs used in the ADI-2 DAC, thus would affect its analog output signal.

However, none of this is an issue with RME's digital volume control!

In fact an analog volume control has a (theoretical) advantage in only one point, namely the maximum signal to noise ratio at a higher level reduction. In reality, current circuitry overturns the theory, and the SNR at the output of such a device is no better than that of a digitally controlled one. This is even more true the better the DA converter works and the less noise it has - just like the ADI-2 DAC, which provides the maximum noise ratio over a wide level range of 20 dB, thanks to its four reference levels realized in the analog domain.

The most often cited issue of a digital volume control is an alleged loss of resolution at higher attenuation. An example: 117 dB dynamic roughly equals 19 bit resolution. A volume attenuation of 48 dB (8 bit) leaves 11 bit of resolution. Such a simple, but important details omitting argumentation, usually ends with: the music must sound distorted in quieter parts, and the signal to noise ratio is down to a useless 69 dB.

The former is simply wrong, the latter irrelevant in practice. Indeed there is a reduced signal to noise ratio, but it doesn't matter, as the noise was not audible before (below the hearing threshold), and is still not audible after lowering the level. And the reduced SNR also applies to devices with potentiometers, since the potentiometer is never placed at the output, but in the middle of the circuit, followed by further electronics which also add some basic noise.

The quality of the ADI-2 DAC's digital volume control is best shown by measurements. Hard times coming up for convinced supporters of the analog control, because here it is very clear that the disadvantages of a digital volume adjustment, such as roughness and distortions at higher attenuation, simply do not exist - at least with RME. 

The following measurement shows a digital full-scale sine of 1 kHz, 16 bits without dither, which is reduced in level by 40 dB. Also shown are a full-scale sine of 1 kHz with 24 bit, at 60 dB and 96.3 dB level attenuation, which is the lowest volume setting the ADI-2 DAC offers.

A high-resolution FFT like HpW Works makes it possible to disassemble the signal into individual frequencies, and to identify unwanted components down to a level of -190 dBFS. The measurement shows that the undithered 16 bit signal does not produce any distortion or other tones above -170 dBFS. So at a volume setting of -40 dB the measurable THD is -130 dB. At 24 bit a volume setting of -60 dB also achieves -130 dB without distortion. And at a volume setting of -96.3 dB there are still -93 dB THD measurable.


 

These results clearly show that distortion products of the digital volume control are not drowned by the DAC's noise, but are not generated at all. It works perfectly even with an undithered 16 bit signal, no detectable distortion products are produced.

If the volume control is measured at the analog output, the demonstrable THD is reduced to around -100 dB at a volume setting of -60 dB, by the self-noise of the DAC (SNR 117 dB RMS unweighted). In the above measurement that would be seen as straight noise floor at -160 dBFS. The digital volume control of the ADI-2 DAC therefore works much more precisely and cleaner than required for current top-level DACs.

In summary:

RME's digital volume control in 42 bit TotalMix technology avoids all the disadvantages of analog level control via pots, is easy to use, offers reproducible settings, and the highest sound quality.

 

(from: https://archiv.rme-audio.de/download/adi2dac_e.pdf)

Wow, given all that, this should be a giant killer, equal to or better sounding than all others. I haven't had the opportunity to hear an RME, but from anything I've read, they are not all that, sonically.

[audiobomber]

7 hours ago, Abtr said:

 

Hmm.. Not sure where you read that. I've only seen very good reviews regarding the sound quality of the ADI-2 and IMO it is indeed a very good sounding DAC. It also measures extremely well. I just don't use its proprietary USB input. I use a DDC (Schiit Eitr) for USB, followed by a coax to Toslink converter to the optical input of the DAC. Sounds brilliant.

 

With respect to the digital volume control, 4 analog output level settings are available to maintain maximum dynamic range (-5, +1, +7, +13 dBu) for different operating levels. I used all kinds of volume controls (active preamp, passive resistor based, autoformers) but I prefer the digital VC of the ADI-2. 
 

Sorry Abtr, I shouldn't post when I've been drinking. 🤪 My comment was belligerent and unnecessary.  

 

I did a lot of research on the ADI-2 when I was shopping for a DAC a few months ago. Unquestionably it is a good DAC and well worth the asking price. It did not seem like the DAC for me so I bought a Benchmark DAC3 instead, which sounded so much like my existing Audiolab DAC that I returned it.

 

Here is one of the ADI-2 comments that disturbed me, from Hi-Fi+ Magazine, who know about PRaT: "The RME is a DAC that stresses detail over rhythm". This finding relates to my post on measurements earlier in the thread. From using a couple of DAC's that provided a separate clock link, I know that PRaT is a function of timing, and cannot be described by any measurement I've ever seen (and I value PRaT above all else). It is likely that a USB processor between the digital transport and DAC, as you are doing, would improve timing and therefore PRaT.

[audiobomber]

3 hours ago, Abtr said:

 

Hmm.. I'm not sure what kind of DA-processing would prefer detail over pace, rhythm and timing (PRaT). Aren't timing problems generally called 'jitter'? Maybe you should take a listen to the ADI-2 DAC. Cheers. 

Jitter figures do not correlate completely with pace, rhythm, and timing (or in musical terms, attack, sustain, decay, release). Power supply is also a huge factor in PRaT, not sure what else.

 

The nearest RME vendor is hundreds of miles away, and I'm no longer interested in a USB DAC. I want an ethernet DAC, so I'm not very likely to hear the ADI-2.

[audiobomber]

19 minutes ago, Abtr said:

Yes, I agree, power supply is a huge factor in sound quality. Not sure how an ethernet DAC would improve that..

I want an ethernet DAC:

1) So I can move my sMS-200 to my headphone system. I made the mistake of trying it there instead of my Dell laptop, and I want it back.

2) I suspect that having a common clock for streamer and DAC may benefit PRaT. I have not been able to test this, never having heard an ethernet DAC. The Auralic Altair G1 seems to excel at PRaT from the sonic descriptions I've read.

[audiobomber]

26 minutes ago, xamastrok said:

Is it because a 1300€ machine cannot do everything right and the digital preamp department lags behind?

A DAC/preamp needs a superior analog output stage to drive a power amp properly. 

 

I'm using my exaSound e32 DAC connected directly to my power amps, as recommended by the manufacturer. I would not go back to using a preamp, because the cost to buy a pre that would beat the output stage of the e32 is way beyond what I am willing to spend.