Ultimate Equipment Test!

[Tenson]

We have seen tests where users have been asked to judge the quality of equipment by comparing a recording of it's output to a direct copy of a digital source file. The recent Squeezebox test on PFM was interesting due to the low cost of the equipment.

I think tests like the above mentioned are very stringent because not only are you comparing it to a pure digital source file, but you also include any distortions generated by the equipment used to record the item under inspection.


However lets see how far we can take this...

I have uploaded three files below. File A is a direct bit accurate copy from the CD. File B is played through my DAC, and then recorded by my ADC..... ten times! So that means the file was played and recorded, that file was then played again and recorded again, and again and again... Each time the distortions of the equipment will build up, just like taking a copy of a tape from a copy. File X is a mystery, it is either the same as A or B.

I'd appreciate if you would download each of the three files and listen to them on a quality system. Burn them to a CD if you can't play from the computer. Take your time to listen and don't feel any pressure to be right or wrong. This is a test of the equipment, not of you! Please then vote on which file you think X is the same as. Is it the pure digital rip or is it the the 10x recording? You may also vote if you are not sure.

I'd like to add that I have no preconception about this test. I believe doing it once through the chain is inaudible... but ten times? I'm not so confident as it is a damn tough test!

File A: http://www.mediafire.com/download.php?rexpdbblyec7oie

File B: http://www.mediafire.com/download.php?9aaxwazb6m5ugtz

File X: http://www.mediafire.com/download.php?bt745fafowf42mc

Please Note: This test is running on multiple forums. Please only vote on one forum as I will compile the results later.

Also, the recording is 'We Added It Up' by 'My Brightest Diamond'. I hope no one will object to its use in this test but if you do, please let me know and I'll remove it.

 

[jazid]

Wh'appen here? I arrived a bit late for this (today) but think its an interesting test. Really only one response? As it happens, on a quick listen, I tend to agree with that response, but think the degradation is really surprisingly slight given the processing the signal has endured. CAn anyone throw more light on this test?

 

[Tenson]

Sorry I've been really busy lately so I didn't publish the results. I'll try and do it tomorrow.

 

[Tenson]

Hello everybody!

So across the forums the votes were:

X is A = 16 votes 39%

X is B = 8 votes 19.5%

I don't know = 17 votes 41.5%

Would anyone like to comment on the meaning of this?

I'd observe mostly two things.

Firstly the majority of comments about difference were tonal, and there is indeed a change here. Due to the filtering applied at the low and high ends of the spectrum to remove DC and ultra-sonic noise there is a slight ~0.2dB reduction at the extremes each time the signal passes through. After 10 passed this is about -2dB at 20KHz and -3dB at 20Hz. If the system was expecting to pass the signal 10 times this could easily be adjusted to give a flat response with more gentle filtering. I'd be very interested to repeat the test again and see if those who heard a difference continue to do so once simple frequency response has been corrected.

Secondly, I notice there seems to be a trend depending on the forums. So I think making the results visible before the end of the test is a serious handicap. Most of those who heard a difference on PFM voted A, however WigWam had a nice equal balance (although far fewer participants). Do people on PFM have better hearing or systems?

My view of the results is that a real but slight difference is there, and it is balanced almost perfectly on the limit of audibility. Hence votes were either correct, or in the 'I don't know' camp. If you add up the incorrect votes and the 'I don't know' votes the total is much greater than correct votes. What does that mean?

 

[Markus S]

Were A and B the same on all forums?

 

[Tenson]

Yes.