Pure Music Dithered Volume Control

[timztunz]

I want to see if I'm on the right track with something. I have understood that if you adjust iTunes volume control from any position other than full volume that you start affecting truncation or data loss. But that using the dithered volume control in Pure Music that it does not have that effect on sound quality, that its transparent volume control. Is that correct?

 

Here's the reason I ask. In comparing CD playback to computer playback I've always had the problem of such great disparity in the volume levels of each making A/B comparisons very difficult. Yesterday I listened to the computer with Pure Music set at 0 and I adjusted the the volume at the preamp to 89-90dB. Then I "dithered" down the Pure Music volume to what the CD volume level was at the same preamp volume setting. On the particular CD I was using (Dire Straits BIA W. German Vertigo) this resulted in about a -9 on the Pure Music volume scale. I then increased the preamp back up to 89-90dB. I was convinced that I could hear no difference in SQ between 89-90dB with Pure Music volume set to zero and 89-90dB with Pure Music volume set to -9.

 

How does this compare to what anyone else has found?

 

[timztunz]

I guess no one will accuse this group of being a bunch of dithering volumizers.

 

[PierOz]

It seems that since the version 7 iTunes is using a 24bit dithered volume control:

 

http://www.benchmarkmedia.com/wiki/index.php/ITunes-QuickTime_for_Mac_-_Setup_Guide

 

http://www.wickeddigital.com.au/index.php?option=com_content&view=article&id=97:itunes-setup-for-audiophiles&catid=44:computer-audio-articles&Itemid=222

 

can anybody more knowledgeable than I am can confirm that, specially for the last version which is 9.1.1?

 

[JR_Audio]

I do not know where iTunes claimed that they are having now a perfect working dithered volume control, because they haven't. I do not read press sheets, I listen and measure to confirm.

 

And when I listen also to the latest iTunes 9.1.1 I noticed an sonic degration of the sound so I measured it and that confirms, that iTunes does not have a perfect volume control.

 

See my attachments where you can see also for comparison a perfect dithered non noise shaping volume control and a perfect dithered noise shaping (just one example of noise shaping, there are many possibilities) volume control.

 

Juergen

 

[timztunz]

JR_Audio, per the OP have you also done those measurements with Pure Music to see of they have perfect dithered volume control?

 

[JR_Audio]

Yes I have also measured all dither options with Pure Music, but I can't give you any graphs yet, because I am partly involved in that point. All I can say is, that it is much better than the regular iTunes 9.1.1 volume control and on the way to getting perfect.

 

I would suggest using the Pure Music 4th order noise shaping filter with 24 Bit and 0.75 LSB amount. This will give you a very good resolution and timbre of the sound.

 

The fine thing with Pure Music and level control is, that when you set the slider to 0 dB, you get bit perfect output, and only when you change the slider from that position, dither is added.

 

Juergen

 

 

[timztunz]

Thank you very much Juergen. I was beginning to think this thread was invisible to everyone but me, or that I'm the only one messing around with the Pure Music dithered volume. Neither of which seemed likely options.

 

One more question, when you say "...4th order noise shaping filter with 24 Bit...", does it matter that all of my music (ok, except for two Carol Kidd 24/96 albums) are 16/44.1 and I'm using a NOS DAC? Is there an advantage to using the 24 bit setting to which you refer, over the 16 bit setting option?

 

[JR_Audio]

The bit width of the dither has to be set to the smallest bit width of your digital audio playback system, so when using external DAC to 24 Bit maximum for 24 Bit DACs and to 16 Bit for 16 Bit DACs (or to 32 Bit for some internal sound cards).

 

This is not dependent on the source bit width.

 

So in your case, for your NOS DAC, I think you should set it to 16 Bit (but go to your product manual for further details about your bit width).

 

Juergen

 

 

[PierOz]

thanks for your comments Juergen. it's nice to have a straight and well documented point of view. I should point out though (but that does not question your point) that my first link is from Benchmark's wiki, I guess they've done their measures too, that's why I was prone to believe them.

 

But thanks again for making things clearer.

 

 

 

[barrows]

one other thing to consider when using a digital volume control. Your DAC has a fixed level of noise at its output-this is the inherent noise of the DAC itself I am talking about. The signal to noise ratio of the DAC is achieved as a ratio of a 0 dB signal to the inherent noise of the DAC. When you use a preamp after the DAC to control the volume, the signal to noise level of the DAC is preserved as the inherent noise of the DAC is attenuated the same amount as the signal by the preamps volume control. When you use a digital volume control, whether in Pure Music, or a built in (in the DAC chip itself) volume control, the inherent noise of the DAC is not attenuated, so as the volume is lowered below 0 dB, the effective signal to noise ratio also drops. In practice this degradation is probably not a problem except at very high levels of attenuation (very low volumes). Of course whether digital volume control will outperform an analog volume control will also depend greatly on the quality of the analog volume control-as analog volume controls and preamps vary greatly in resolution.

 

 

[ASB]

Lot of new generation DACs' come with "dithered volume control" function. Weiss and new Northstar DAC, M2Tech DAC for example.

 

Has anybody compared "Dithered digital" vs "analoque" volume controls?

 

If the differences are not audible, it will enable us to new system setups.

 

[bdiament]

In my view, playback volume should be adjusted after conversion to analog, in the analog domain.

 

Most, if not all program material has already been through a dithering process. Particularly with 16-bit source material, adding another dither process will, to my ears, exact a sonic price in terms of "focus", fine harmonic detail and spatial information.

 

Granted, if adjusting volume in the digital domain, using 24-bits will mitigate some of the damage of a 16-bit control but still, I avoid any playback volume adjustment until the signal is analog.

 

Just my perspective.

 

Best regards,

Barry

www.soundkeeperrecordings.com

www.barrydiamentaudio.com

 

 

[JR_Audio]

Also in my view, I prefer a good analog volume control after the DA process over a digital volume control in the playback path. Even it is perfectly dithered, will compromise the sound to certain extend. Also I am not a fan of very high psychoacoustic shaped dither processes, because, at least in my experience and taste, it changes also the sonic character of the instruments and sound stage. Some “smooth” noise shaping, that leave the signal from 20 Hz to 10 kHz untouched, sound better than unshaped dithering to my ears, but the dithering that take the most out of the 3.5 kHz region, are not my favorites. At the end of the mastering process, you have to use some kind of dither to finalize to 24 Bit or even 16 Bit, but when a product is already finalized, I prefer using analog volume control.

 

Juergen

 

 

[barrows]

going to be better is impossible to predict, as there are so many variables. In many cases a digital volume control may cause less signal degradation than analog, but the real answer to this question is: "it depends". Analog volume controls come in many forms: simple resistive pots, chip based resistor ladders, discrete resistor ladders switched by chips, discrete resistor ladders switched by silver on gold contact relays, discrete resistor ladders switched by silver on gold contact rotary contact switches, and even preamps that feature adjustable gain to control volume instead of an attenuator (like the $18K Ayre KX-R). All of these types of volume controls vary in how much (and what kind of) distortion/noise they add to the signal.

Of course, using a digital volume control will allow some people to take a preamp out of the signal chain entirely (removing any distortion/noise introduced by the preamp itself, as well as the extra interconnect and connections). The advantage gained by the shorter signal path with no preamp may be bigger than any sonic degradation introduced by using the digital volume control. With no preamp one must consider the output capability of the DAC: is the DAC's output stage up to the task of properly driving the input stage of the amplifier? Many DACs do not have nearly as good an output stage as a good preamp, in which case trying to drive an amp directly will result in a loss of dynamics and body.

The bottom line when deciding to use a digital volume control from a DAC direct into an amplifier (or a DAC direct to an amplifier which features an analog volume control) is that one must try it to see how it sounds, and then try it with a preamp as well, to see if that sounds better. In my experience, a really good preamp often (but not always) will improve the sound, especially in terms of dynamics, bass response, and body.

 

[bdiament]

Hi Barrows,

 

An exception of course, would be a DAC with an analog volume control. The preamp is removed from the chain, yet volume control for playback remains in the analog domain.

 

The LIO/ULN-8 for example, has a digitally controlled rotary encoder which controls an analog volume control at its output.

 

Best regards,

Barry

www.soundkeeperrecordings.com

www.barrydiamentaudio.com

 

 

[barrows]

I believe I addressed that possibility in the final paragraph of my response above. It is still possible (even likely in my opinion) that a really good preamp will improve the sound of a DAC featuring an analog volume control, as the output stage of a really good preamp may better drive the input of an amplifier to produce better dynamics, bass response, and body. I am not saying this is always the case though, hence my advice is for people to try out their options, especially if they already own a really good preamp.

 

[bdiament]

Hi Barrows,

 

I agree: trying out the various options is always the best approach, as the results will vary depending on the component(s) involved.

 

I must say though that for my ears, I'll take the flaws of an analog volume control any day over the results of using a digital control for playback volume. The best I've heard, however, is no volume control at all. Unfortunately, that is true only in exceptional circumstances and is not a practical solution; I have only one or two recordings where it doesn't become a dangerous proposition. ;-}

 

Best regards,

Barry

www.soundkeeperrecordings.com

www.barrydiamentaudio.com

 

 

 

[4est]

and how this relates. I think I am confused. Mainly the amplitude resolution part.

 

From Pure Music users guide:

 

"At Monitor volume settings below 0 dB, dithering may optionally be applied:

A 64 bit pseudorandom number generator (PRNG) with an extremely long sequence

repeat length is used to generate the dither in real-time, instead of using a “canned,”

repetitive dither sequence. The Uniform dither option is the suggested choice,

and the optimum setting of the slider is 0.75 LSB. The LSB word length should

be set to 24 Bit, unless using a DAC with only 16 bit resolution (very unusual) or

capable of 32 bit integer word length (very unusual). (Many audio interfaces

simply report the canonical CoreAudio 32-bit ?oat format in Audio MIDI Setup,

instead of the true internal integer format of the DAC.)

 

The Amplitude word length setting (16, 24, 32) only affects the dither amplitude.

All volume adjustments in Pure Music are made at 64 bit resolution, regardless

of the Amplitude setting.

 

 

Other options are provided for those who prefer noise shaped dither. Moving

from the Uniform to the 12th Order Noise Shaping options, the dither energy

becomes shifted to increasingly higher frequencies, and a narrower frequency

range. More CPU cycles will be consumed when using noise shaped dither.

 

 

Stereo (uncorrelated) dithering uses dual PRNGs to generate the dither indepen-

dently for each channel. Deselecting this option causes the same dither to be

applied to both channels. The Stereo setting is recommended."

 

[JR_Audio]

Do you want to know how dither is working or do you want to know how you work with dither?

 

In the first case, I would recommend reading some AES papers especially from Stanley Lipshitz. He has some very good papers, explaining the basics of dither.

 

In the second case, just take the advice from Rob in the Pure Music User Guide or just what I have written above.

 

Juergen

 

[4est]

Thank you for your response. My question was more if there is a helpful difference if the internal adjustments are calculated at 64 bit, then converted to 24 (or 16/32). You see, I an stuck with a digital volume control a the moment. I am running a Weiss Dac2 straight into an amp. Presently I do not have a line stage that surpasses direct connection, and I have too much gain. Therefore, I now have double dithered volume controls. I am at loss as to which to use. I could build/buy an attenuator, but this set up will exist for only another couple of months or so in a mediocre set up (my present front end far eclipses the associated components). I am amazed how much I am already getting out of this, but if more can be had- well, I am all ears!

 

[JR_Audio]

I suggest strongly using only one of the two possibilities for you for using digital volume control.

 

The Weiss DAC2 has also the possibility to adjust the analog max output level to match different power amps and speaker sensitivity, so you can easily reduce the maximum analog output level with the small rotary switch on the back.

 

Daniel Weiss does use often the POW-R dither algorithm that in the higher order, I personally not a fan of. Using POW-R1 is still ok (for my ears), but if you are going to POW-R3, I personally do not like this much. I also do not know, what kind of dither is used in the DAC2 and if there is a possibility of choices.

 

I must add here, that this is my personal taste, and that are many out there, who do like the higher order psychoacoustic optimized dither, so it is up to you, what kind of dither you prefer.

 

In your case I would reduce the maximum output level of your DAC2 on the analog side and then decide via listening, whether you like the Weiss dither better or the pure music dither. The 12th order Pure Music dither has some similarities with the POW-R1 dither, not the same, but something in common.

 

So look in your Weiss manual if you can choose what kind of dither or try the different dither in Pure Music. But as I told above, dither is also a question of taste, so try yourself, and it is also dependent on the music style. So give it a chance and decide yourself.

 

Juergen

 

[4est]

Right now the analog attenuator is at the lowest setting, and I still have too much gain. Presently, my Weiss is set in so that I may use Odb on Pure Music when listening loudly to my best recordings. The problem is, that then many "less dynamic/more compressed" cuts are too loud. I find myself listening at -6 to -12 db in pure music with some cut (dither) on the DAC2 as well. Sounds like I need to build a resistive one. Part of the issue is that I am using very efficient speakers with a bigger amp. Things sound pretty good for what it is! I must add that I did notice a pleasant difference when I took your suggestion to try the 4th order dither. Thank you for your help!

 

Forrest

 

[Audio_ELF]

Not sure if this really is significant, but Weiss have for a while extolled the virtues of digital volume over analogue; but then produce a rather expensive transformer volume control (TVC). Does this imply they now feel a digital volume can be beaten with a transparrent analogue volume?

 

Eloise

 

[ASB]

Thanks Juergen, Barry.

 

I have talked to a friend of mine who has a Weiss Minerva. He said he has tried Dithered Digital Volume control but ended up disabling it.

 

He says it is sounds much better using his pre-amplifier as volume control.

 

[ASB]

With DAC202, Weiss has an analog volume controlled DAC for the first time.

 

Most probably next generation Weiss devices will also have analog volume control.