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To Dig or not to dig, that is the question

March Audio

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Ok, there has been some discussion regarding digital volume controls. There is naturally a degree of audiophile nervosa on the the subject. To this end I purchased a high quality Alps log 100k analogue pot and bashed together a volume control box. The idea to compare the signals to digital volume control. I havent had time to do what I intended, but a very quick and dirty comparison is below. Please dont regard this as anything definitive, more to provoke discussion. This really needs to be done on Amirs APx555.

Just for fun, you tell me which are the analogue volume, and which are the digital volume plots.

I generated a signal in Adobe Audition. It consisted of 5 sine tones at 1kHz, 4.3kHz, 5.8kHz, 8.2 kHz and 10.05kHz. The 1kHz was at about -45 dBFS and each subsequent tone reduced in level by a further 10dB. The reason for startin g at a low level was to ensure that the DAC harmonic distortion was already below the noise floor so as not to cause any confusion. Measurements were then taken at reducing 10 dB levels (it was a challenge to get the pot precisely adjusted) until the lowest signal disappeared into the noise floor (about a further -60dB attenuation.). Oh btw, 20 dB of gain was added in the measurement input to try and keep the dac noise floor above that of the measurement system. I will show 20dB steps to reduce the number of plots.

p1.jpg


p2.jpg




Volume control type A

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Volume control type B

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vitalii427

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I guess B is analogue pot. Because of two strange harmonics (8k & 16k) above the noise floor with no signal. I see no other difference so just guessing.
 

solderdude

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I think showing L-R tracking at -60dB may be more conclusive. :cool:
Have to admit that the few RK27 pots I have been using track quite well even when attenuating so much I can barely hear anything.

My guess would be B is the digital one as resistors don't produce harmonics.
Besides... the RK27 has a 'A' taper and A stands for Analog as well so that logic says A has got to be analog.
Unless you are trying to fool us ans chose A for 'digital' and the 100k pot picks up some 8kHz noise some how.

In either case... there does not seem much to worry about as long as one stays below the max input level of the digital control when it comes to distortion.
 

solderdude

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Can I also water my garden with those ?
They seem a little short for that duty and on top of that don't seem to have the correct couplings.
 

Veri

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Sorry should have used this internally. Its like veils are removed from the sound, your can hear into the depths of blackness. It makes emotion pour from the speakers ;)

View attachment 19615
Would you look at that "accessible" price level man! very low price of admission to enter the "quantum realm" of music enjoyment ;) ....
 

derp1n

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Just give us the answer you cocktease.
 

Krunok

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I guess B is analogue pot. Because of two strange harmonics (8k & 16k) above the noise floor with no signal. I see no other difference so just guessing.

My guess as well, A is clean so probably digital. :)
 

rebbiputzmaker

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B is digital volume and this realistically proves little imo.
 
OP
March Audio

March Audio

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A is digital and B is analogue.

This test needs to be repeated on a Apx555 so we can see the very slight change in noise floor at lower attenuation levels with analogue. Basically the performance of digital volume exceeds what you can hear and in real world use is no worse than analogue. In fact it knocks analogue into a cocked hat with regard to things like channel balance.
 

Thomas savage

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Funny enough my analogue pot seem quitest when on full volume . You can hear a reduction Of hiss at the tweeter. With ear right up to it nothing audible at MLP.

Well implemented digital attenuation to me would be preferable. On my to-do list.
 

Thomas savage

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B is digital volume and this realistically proves little imo.
This is just a excise in curiosity, no claim here it would prove definitive in fact the opposite has been expressed from the start.

And it seems you guessed wrong, don't worry you will recover.
 
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