Minimum recommended volume setting for Directstream?


#1

I guess, really, this is a question for Ted: just wondering if the S/N, dynamic range or distortion start to deteriorate at lower volume settings on the Directstream? I know this can be the case for some types of volume control in the digital domain, and I’m curious whether it applies to the Directstream at some point and the low output setting should be used.

Thanks in advance.


#2

Iirc it’s made mention in the manual that there is some 20bits of headroom for volume so the should be no detriment to the audio bits


#3

It’s complicated - there’s no digital loss with lower volumes, all input bits and volume bits are used/represented in the one bit output. On the other hand the DAC itself has an analog noise floor. The 20dB analog attenuator is there so that if you normally listen at volume setting of 60 or lower you can engage the attenuator and listen at 100 or lower and have a 20dB lower analog noise floor.


#4

“The 20dB analog attenuator is there so that if you normally listen at volume setting of 60 or lower you can engage the attenuator and listen at 100 or lower and have a 20dB lower analog noise floor.”

I’m not following the above. Can someone re-explain. …It’s 20 db lower below 60 and 20 db higher above 60?

Thanks.


#5

Aar

The 2xDSD digital signal at the output stage of the DAC has a certain noise floor. For simplicity of explanation, imagine that it’s 100dB lower than the maximum signal level the DAC can create in the audio band below 20kHz, but it rises through the octaves above that to be a whole lot of ultrasonic noise. (The actual noise floor is lower than -100dB, this is just an easy figure for illustration.)

The passive, analog low-pass filter stage is designed to let all the content below 20kHz pass through (both the desired audio and the noise floor) and then as the frequency rises impose greater and greater limitation on the unwanted ultrasonic noise so that a minimum amount of it reaches your amplifier.

The shape and level of that filtered noise is fixed. It doesn’t alter when you adjust the volume setting of the DAC. Even if you are playing no audio, that noise floor is still leaving the DAC and heading to your amplifier.

Now let’s imagine you have a piece of music which peaks all the way to the maximum digital signal level. If you have the DAC volume set to 100 and the attenuator off, the peaks of the music will be stretching the output of the DAC to its maximum level. Since we have a noise floor roughly 100dB lower than that, your signal-to-noise ratio there is 100dB. Awesome.

But your amplifier and speakers might take a signal at that level and produce a sound that’s way louder than what you want to hear. So you turn down the DAC volume control, way down to 20. Each volume step on the DS DAC is half a dB, so -80 volume steps is -40dB in signal level. But the noise floor hasn’t changed. Your signal now peaks at 40dB below maximum, and your noise is still there at 100dB below maximum, so your signal-to-noise ratio has dropped to 60dB.

If your amp and speakers are very sensitive, this can happen and the noise becomes intrusive in your listening experience. So, here comes the attenuator.

The attenuator takes the analog output of the DAC and throws some of it away. 20dB worth of it. Doesn’t discriminate between audio signal and noise. Everything gets 20dB quieter, including the noise. Reaching the same listening level requires you to turn the volume control up to 60 (adding 40 half-dB steps for an extra 20dB of signal) but your noise doesn’t get any higher. So now you are listening to the same signal but with the noise 20dB lower. You now have a signal-to-noise ratio of 80dB instead of 60dB.

This increase in SNR at the same volume only applies if you normally listen with at least 20dB of unused headroom – ie with your volume set to 60 or lower, meaning you are able to increase to 100 after enabling the attenuator.


#6

Perfect. Thanks for the great explination!


#7

Since there is no loss bits, does it mean this is all about S/N ratio?

I listened at volume 100, Preamp volume 20-35. When I engaged the attenuator, and volume still at 100, preamp volume changed to volume 40-60 for normal listening volume, the overall sonics is more relaxed and 3D and less edginess. Not sure what this means, and whether preamp quality has a part to play here…

Any insights appreciated.


#8

I have read but have only a little experience with the following, however, the experience that I have tends to corroborate the claim:

Paul (and a few others) has commented that the volume control in almost all preamps does noticeable harm to the signal quality. This is kind of a given and most pramp designers put some effort into minimizing this. Along with that, the volume controls in most preamps tend to work better or do less harm at higher volume / lower attenuation settings. This again is something of a given and effort is put into minimizing this effect also.

It has been mentioned before that if you are truly pursuing the best audio quality in your system, you should experiment with different combinations of more or less attenuation in your DAC (or whatever other source you might have that has a variable output level) and less or more attenuation in your preamp volume control. In my system with my PerfectWave DAC, I set the DAC to 100 and adjust the preamp volume to the absolute max that I would normally listen to. Once there, I adjust the playback level with the level control in the DAC, as it is the easier and more accurate of the two to adjust remotely. This has the PWD working in its upper range (minimum attention / minimum possibility of bit loss / maximum dynamic range) and the preamp nominally fixed at about 55~60% of its level control. With this combination, I feel that I get a subtly better quality than simply setting the DAC to 100 and adjusting the playback level with the preamp volume control. I have not seriously experimented with setting the DAC level lower and the preamp level even higher, but with my ears and my system, these adjustments had no significant effect so I just stick with my initial setup. I quickly tire of tweaking and just want to listen to the music. :slight_smile:

As is said about all things audiophile, you must experiment with your own system to hear what set of tweaks it and your ears prefer.

[edit]
To clarify, the experience that my comment is based on is with the PerfectWave (PCM) DAC. The DirectStream (DSD) DAC is a little different in that you can run the volume much lower (greater attention) before you hazard any digital or noticeable audio degradation. The primary loss with the DirectStream DAC in reducing the output level is in reducing the signal to noise ratio. Also, the DirectStream DAC has a 20dB attenuator built in that adds one more variable into the mix. With the DirectStream you may get the best results with a lower output from the DAC and even higher volume control setting on the preamp. Again, the audiophile caviat of having to try it with your own system is in effect.

J.P.


#9

Winston Chia, I read your post with interest. I have owned the DS DAC for over a year but hadn’t played with the attenuator switch until last week. My experience is similar to yours. The music is less forward and there seems to be less noise or glare. Also more spatial balance and depth. At first I thought there was a loss in verve and bounce, and less extension in the high and low registers. But after listening this way for about a week, I’m not so sure. These things are relative to everything else going on in the presentation, and when I switch back briefly to the High setting, I find it to be too much. I am using an integrated SET amp. I asked the guys at Cary if this amp is considered sensitive, but they said it’s no more or less sensitive than most. They said the preamp section adds 20db, so if the DAC attenuator takes away 20db, then maybe everything balances out. Maybe it’s right where it ought to be.


#10

Concur with what Winston said …

I listen always with the attenuator on … with the volume at 100 … and the preamp at 50-70. The sound is much warmer and cleaner

Without the attenuator the sound is harsh, forward and somewhat lifeless …


#11

Strange… I find a much better musical presentation with the attenuator in the off position. With it engaged… the musical presentation becomes dull and lifeless,as if someone pulled the plug on the sound and deflated the venue. surprised-014_gif


#12
mark-d said Strange... I find a much better musical presentation with the attenuator in the off position. With it engaged... the musical presentation becomes dull and lifeless,as if someone pulled the plug on the sound and deflated the venue. surprised-014_gif
+1

#13

And both methods are entirely correct.


#14
mark-d said Strange... I find a much better musical presentation with the attenuator in the off position. With it engaged... the musical presentation becomes dull and lifeless,as if someone pulled the plug on the sound and deflated the venue. surprised-014_gif
Bootzilla said
mark-d said Strange... I find....
+1
I think engaging the attenuator means almost a necessity to nearly double the analog preamp volume to get back the general listening volume....would be interesting if you try this (if not already done so), and report your findings :)

#15

I have done what you speak of… Still not to my liking. To my ears the music just sounds to dull and uninvolving. If one had an overly bright sounding system I guess it could make a difference in a preference for the attenuator engaged. Like Elk said…“both methods are correct”. One way does not mean the other way is broke. I just like the attenuator in “my system” turned off.


#16

Use of the attenuator is probably the most system dependent part of the DS - as with all things audiophile one needs to check which way is better for oneself.