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Use Foobar volume control VS 50k Pot as preamp, Wondering if using digital volume control or the pot in my trends audi
Digital volume control or physical preamp
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grkn
post Aug 27 2008, 18:07
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So I'm using foobar to pass a optical signal to my DAC, and then the DAC lineout goes to the TA-10.1 that I can choose to use as a poweramp bypassing the pot.

What solution do you think would be better? I'm ill equipped to do any blind testing myself.
If using foobar volume control I need to limit volume approx -25dB smile.gif And that's a bit scary, as I could possibly damage my speakers if I put it to max rolleyes.gif

Any thoughts? And is Foobar volume control better than say Mediamonkey? (only foobar can do 24bit output, and that has something to say...right?)

This post has been edited by grkn: Aug 27 2008, 18:14
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Slipstreem
post Aug 27 2008, 18:46
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I've gone for "even a pot is better" on the basis that you're guaranteed no loss of resolution in terms of bits by taking the analogue approach. I'm not familiar with the exact equipment you're using, but if the final amplifier has a built-in analogue potentiometer for volume adjustment then you're probably best off using that.

Alternatively, make a pair of fixed potential dividers (one for each channel obviously) using metal oxide resistors to give you the initial 25dB of attenuation before the analogue signal enters the amplifier and continue using the input you're using if the tiny difference made by a well implemented digital volume control is of no consequence to you.

Assuming that we're talking about 25dB in terms of voltage ratio, a series chain consisting of a 47k resistor and a 2.7k resistor with the latter at the ground end would give you almost exactly 25dB of attenuation at the mid-point with an input impedance of ~50k and good tolerance to being loaded with a similar 50k impedance load. smile.gif

Cheers, Slipstreem. cool.gif

EDIT: After reading your question again several times, I feel that I may have misinterpreted it. Apologies if I have, but the maths still stands.

This post has been edited by Slipstreem: Aug 27 2008, 19:04
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grkn
post Aug 27 2008, 22:02
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Thanks a lot, decided to dig around after any information proving that outputting at 24bit and using digital volume control ain't so bad:

QUOTE
"Secondly, working in floating point, and dithering the output at 24bits, you lose nothing by reducing the volume of a 16-bit signal input by up to 48dB. In theory! You have 48dB "to work with" before losing data, but it's less than this since the dither noise will add. Further, if the original 16-bit dither+quantisation was noise-shaped, but the dither you apply to the 24-bit version isn't, then you have less still.

Beyond this, your D>A and associated electronics will have a fixed noise floor. By reducing the volume of what is contained in the digital input signal, you are sinking further into that noise floor. Whether this is relevant depends on the noise floor, the original recording, how much you reduce the volume, and yourself.

If the listening volume ("analogue" gain setting) is such that the noise floor (with dither) of the D>A is inaudible, then in theory no audible harm can be done by any digital reduction of the volume (e.g. what you lose in the digital domain by reducing the volume by 80dB would be inaudible had you chosen to reduce the analogue volume by 80dB!)

In practice, a less than perfect DAC could do damage (e.g. via distortion), but then in practice the signals which you attenuate digitally the most (i.e. the ones which are loudest in the first place) probably have least to lose.

In short, don't worry about it. Unless, if course, you find the noise floor of your 24-bit D>A is similar (or worse than!) that of a 16-bit recording - in that case, abandon this idea!

Cheers,
David."


http://www.hydrogenaudio.org/forums/index....showtopic=47597

So, seems like using KS and outputting at 24bit might do the trick? We're "only" talking about -25db here smile.gif

This post has been edited by grkn: Aug 27 2008, 22:03
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