Win7 volume control - good enough or still need preAmp? - diyAudio
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Old 27th May 2010, 08:23 AM   #1
Galgo is offline Galgo  Israel
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Default Win7 volume control - good enough or still need preAmp?

Hi guys,

I've recently built a 6ch amp for my HTPC based on 3X Tripath TA2020.
I'm trying to improve the build by optimizing the signal path and remove unnecessary components such as the "volume control" pot (which should be for 6ch or 3X Stereo units...)

I currently feed the amp. with analog line level directly from the o/b sound based on ADI AD1986a aka. SoundMAX codec (motherboard is ASUS M2NPV-VM).

I might add an external sound card or just a DAC for better Stereo quality and feed it digitally from the PC (this M/B has digital outputs as well or I might go for a USB solution).

My current concern is regarding the quality of the Windows 7 volume control.
It's very convenient and I can easily balance between different channels, some DRC etc. with the remote control I already have...
I know that MS invested significant resources to improve the sound quality of Vista/7 and the digital volume control algorithms are pretty sophisticated.

So what do you think - do you still recommend some "pre amp" as separated volume control (i.e. some basic ALPS pots or go for one of the DIY kits) or will it just interfere within the signal path so I'll better stay with the PC volume controls ?

Any insights/suggestions/links will be appreciated,
Gal

P.S. - The PC is the only sound source and I don't intend to use the amp. with other setups...
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Old 27th May 2010, 08:56 AM   #2
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Hi!

As far as I know, digital volume control in the pc is always achieved by reducing the bit-depth of the signal. This is quite ok, if you adjust the volume from the pc in the upper one-third of the volume range. But the problem is, with no preamp (volume pot) at all, you have to stay in the lowest adjustment range most of the time for "normal" listening levels, and that means you will get a heavily quality-reduced signal out of the pc most of the time.

I use a passive pre (blue Alps pot) between my external dac and my power amp to make a pre adjustment, then I can adjust the volume from the pc (via wireless mouse) in a comfortable range without such a great loss of quality. This works perfectly for me.

By the way, in case you've never heard of it, here's a small and very useful application for the pc to adjust volume with the mouse wheel:
Volumouse - control the sound volume with a wheel mouse

Regards!
martin

Last edited by martinbls; 27th May 2010 at 08:58 AM.
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Old 27th May 2010, 11:29 AM   #3
Galgo is offline Galgo  Israel
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Thank you martin for the informatin and the link

Quote:
small and very useful application for the pc to adjust volume with the mouse wheel
It's a really cool application but I already have almost total control on the HTPC with MCE remote kit (and other equipment using the IR blasters) so no need for mouse interface...

Quote:
digital volume control in the pc is always achieved by reducing the bit-depth of the signal
Is this still true in Vista/ Win7 !?
Quote:Vista will adjust the volume using internal floating point values rather than integer. So it does not reduce resolution as XP did.

Another good read: An audiophile’s look at the audio stack in Windows Vista and 7

In any case - If a "pre-amp" is unavoidable - what will be the best way to do it? (in order to get significantly superior quality than just using the Win7 controls...)

- Integrate the pot in the amp chassis ? (exposed to internal "noise" but close to the amp. input)

- Building a separate "passive" component with the pot shielded and wired on top of the 3 stereo line signals?

- Using an "active" pre-amp kit - i.e.
Crystal PGA2311 Volume remote control preamplifier kit
(Or any other recommended kit - on budget please...)

- shall I use one 6 Channel pot like:
alps-100kx6

Or better to go with 3 separated 2ch controls such as:
ALPS 09 Potentiometer

Cost is pretty much comparable...

Any other insights, suggestions, etc. ?
Gal

Last edited by Galgo; 27th May 2010 at 11:32 AM.
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Old 27th May 2010, 12:00 PM   #4
Galgo is offline Galgo  Israel
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If I'm getting it correctly (from the links I've posted above) - they solve that exact issue by up-converting all audio streams to 32bit before processing:
"...
The new audio stack automatically upconverts all streams to a 32-bit floating-point sample depth (the same that is used in professional studios) and mixes them with the same precision. Because of the amount of headroom that comes with using 32-bit floats, there is no more clipping when playing two samples at the same time. There is also no loss of resolution when you lower the volume of a stream...
..."

So !?!?!
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Old 27th May 2010, 12:07 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Galgo View Post
..........There is also no loss of resolution when you lower the volume of a stream...
could you explain this to me?
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Old 27th May 2010, 12:20 PM   #6
Galgo is offline Galgo  Israel
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Hi Andrew,
I'm not an expert (far from it to be honest)-It was a quote from the link I previously posted:
An audiophile’s look at the audio stack in Windows Vista and 7

It's probably explained better there (easy and recommended read)- but in my laymen words, since they process the audio stream in the unconverted 32bit domain, there is enough headroom to maintain all the original sample resolution (24bit) even if you lower the volume level...

Can anyone verify?
Gal
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Old 27th May 2010, 12:20 PM   #7
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If you want to listen to music , the first is to use a kernel streaming or an asio driver , which just bypasses this upsampling madness they have. You'd better have a DAC with 126 SNR btw.
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Old 27th May 2010, 12:24 PM   #8
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So you can do the same upsampling trick with any of the oversampling plugs available for foobar and etc. You just set 24bit /88khz. Then the DAC probably will distort ten times more , but its worth it. You want to use a good sigma delta DAC tho.
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Old 27th May 2010, 12:46 PM   #9
Galgo is offline Galgo  Israel
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Quote:
Originally Posted by tritosine View Post
If you want to listen to music , the first is to use a kernel streaming or an asio driver , which just bypasses this upsampling madness they have. You'd better have a DAC with 126 SNR btw.
Hmmmmm... I missed that part that ASIO bypass all this... How about using WASAPI instead? maybe good enough and still gives the benefit of that Upconvert "madness" (btw - I think it's completely different than up-sampling and shouldn't change the raw data...)

Quote:
Originally Posted by tritosine View Post
So you can do the same upsampling trick with any of the oversampling plugs available for foobar and etc. You just set 24bit /88khz. Then the DAC probably will distort ten times more , but its worth it. You want to use a good sigma delta DAC tho.
My main concern is that I'll need to control multiple (6ch) audio streams and not only 2CH stereo music...

I might add a DAC in the near future to improve the 2ch stereo music - but I'll still need to control the volume level.

I won't mind doing some more DIY or adding a PCB or two if you can recommend something decent (Preamp / DAC combination?).

I already opened a related discussion on that matter so will appreciate if you could reply there...
Upgrading a "mocha JY-M2" multi channel DAC?

Please consider that I'm on a tight budget and would like to keep my setup as compact and minimal as possible - so would like to avoid purchasing additional devices such as A/V receivers (to decode multi channel audio streams) or an expensive commercial Preamp / DAC.

Thank you,
Gal
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Old 27th May 2010, 12:57 PM   #10
AndrewT is offline AndrewT  Scotland
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Question Digital. Do I need to understand it?

the linked paper used 10% (-20dB) and divided the effective bits by 10.
Then compared the effect of adding 8bits, an extra 256 levels.
Did he forget to divide those extra levels by the same 10?
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