Do modern DACs sound different from each other? [And what about analog RCA cables and USB cables?] Many audiophiles and professional magazine reviews claim they differ audibly but I have my doubts based on controlled experiments such as the one done at Tom's Hardware
comparing a $2000 DAC vs. one that's about $2.
Obviously it would be impossible to test every single DAC against every other one, but I have another test. Let's test if a very common and inexpensive one, the $7.99 Apple iPhone DAC, A1749 (aka “Lightning to 3.5 mm Headphone Jack Adapter") is audibly perfect playing music, i.e."transparent", or if instead it in some way alters/distorts/obscures details in the music passing through it in some discernible way. I have set up just such a test to determine this, which anyone with web access is invited to participate in, and it is completely free. [Internal pics of the DAC and its long model number appear in "Step 9" here
This is based on a test called an SWBT (straight wire bypass test) or A/B Bypass Test. "Straight wire with gain test" is the similar amplifier version. Peter Walker of QUAD, Stewart Hegeman of H/K and Eico, and J. Gordon Holt, founder of Stereophile magazine, were all proponents of this test design. Here is how it works.
To test how accurately an audio device passes music from its input to output you conduct a blind listening test where you compare the device being inserted into, versus removed from, a stereo system's signal path while the device is set to “unity gain”, i.e., the volume level in is the same as the volume level out, measured precisely. Done.
These two signal paths, A and B, are compared under double blind conditions to be sure there is no cognitive bias influencing the listeners. The free download Foobar, with its ABX component installed, let's us compare two digital files prepared this way.
It is important to understand that a DAC and an ADC are the exact same thing but work in opposite directions. If you take the output of a DAC and send it to an ADC the signal goes: D to A to D. There should be no alteration if the DAC and ADC are both "perfect". That's what we do in this test for File B whereas File A is the original, untouched digital signal. File A is the "master" or "reference". So File A is Digital and File B is "Digital, to Analog, and back to Digital". Our test is: D versus "D to A to D". Do they sound the same or do they sound different?
Here are the two files' signal paths to be compared in Foobar ABX. Note that digital File A, the Reference or Master, is left in its original, pristine condition from start to finish and is never re-recorded nor adjusted. It is exactly as it appeared on the CD without alteration.
Reference digital song file (or a bit-accurate 30-sec. excerpt if posted online for legal reasons) --->
Played back on a High Quality DAC in the listener's preferred system.
Master digital song file (or a bit-accurate 30-sec. excerpt if posted online for legal protection)--->
Digitally transferred to my Apple iTunes folder-->
Digitally transferred to my iPhone X via Apple's free USB cord-->
Manually played on the DUT (device under test), an Apple A1749 DAC, $7.99-->
Monoprice 3.5mm stereo mini-plug to RCA jack adapter, $.67 -->
Monoprice 6ft. RCA cable 659, new, $1.05 (it was $.87 ea. when I bought ten of them on sale)-->
Hosa YPR-102 1/4" TRS to Dual RCAF Stereo Breakout Cables, $4.45 x2
Behringer UMC204HD 4-in-1 USB interface (Stereo XLR mic preamp, Headphone amp, DAC, ADC), $79.95 (when I bought it) being used with its best quality "insert" inputs to its ADC -->
Free, basic USB cable the above ADC combo box came with-->
Anker 4-port USB Hub-->
My Asus laptop's USB port-->
Audacity digital recording software, free -->
Audacity digital editing to adjust the recording's level and time sync to match the original file-->
The song is exported in 16-bit/44kHz PCM wav format to my laptop's hard drive as a NEW file-->
This recorded (and original Master) files are uploaded to Dropbox for ABX testers to access-->
Played back on a High Quality DAC in the listener's preferred system.
See the over dozen extra steps
in File B, including passing through the inexpensive DAC? It is my contention all of those steps do technically degrade the sound ever so slightly, but by such a small amount they are audibly “perfect” or “transparent” to the ear. That is, everyone's ear, through any system.
UPDATE 05/06/20: File A
is the CD digital sound and File B
has additionally passed through this chain, including the $7.99 white DAC:
These extra steps, at least to my ears according to the ABX test, are indeed transparent. Give it a go yourself and post your complete score sheet, including its verification number along the bottom, to show how you did.
In a normal 16 trial Foobar ABX test, statistically speaking, a test score of more than 12 correct shows a strong likelihood the discernability was not merely due to chance. [It shows a p-value less than 0.05, which most agree is statistically significant.]
At the time I prepared the test the first person who had agreed to take the test got to pick the specific music of his choice, a well recorded Gershwin tune which I then bought as a CD. Another person expressed some interest in taking the test at the time too. The test taker made a great choice, in my opinion; the well recorded CD has nice dynamic contrast and a broad range of frequencies.
This test is just phase one. Assuming people find my recording chain is indeed “perfect” to their ears and indistinguishable from the master file, based on their posted, complete ABX score sheets-- a validation my overall test protocol works--then I plan to insert my mid-fi AVR into the recorded File B's overall signal path as well, to test its transparency. I may switch to an easier to use conventional DAC as well. Recording this little dongle one via a touchscreen device my klutzy fingers have trouble operating, manually, is an awkward process for me, but I'm glad I have now done it.
There is a video on all this in the works.
UPDATE 04/30/20: A video authenticating each file is now posted later in the thread
The video shows each file's SHA-1 right as I create each files so readers can verify the files I uploaded for testing are indeed the exact same files you see me create in the video. Their authenticity can be tested by anyone by checking that their SHA-1 "digital fingerprints" match what I state they are as I create them. Any alteration or substitution in a file would be revealed by a different SHA-1 number. This verification can be done with various programs or on-line calculators such as the free one you see me using during the file creation process at www.md5file.com
Originally Posted by m. zillch
More info appears in the Dropbox download folder's READ ME file, linked to below. The two files, A and B, are explained and identified here.
Exact Audio Copy of the CD's track 04, cut down to 30sec. in Lossless edit mode:
Above "File A" after passing through an Apple $7.99 DAC, Monoprice ~$1 analog
RCA cable, and converted back to digital via an ADC connected by a free USB cable:
The question at hand is "Are the dirt cheap DAC, analog RCA, and USB cables audibly perfect, aka 'transparent'? Or do they in some way alter/degrade the sound?" The Foobar ABX test determines under double blind conditions if a listener can detect an audible difference between Files A and B, and if so with what level of statistical significance. The SHA-1 of the files are listed on the final score sheet to verify the correct, files were used. [I accidentally grabbed the wrong file at one point during the production myself, after all, but luckily I caught my mistake.]
The two ABX files and a READ ME file are found in this free Dropbox download folder. At this link you may be invited to sign up for a Dropbox account, however there's no need to in order to download the files. Just ignore their ad and scroll to the bottom (or the side?) to find the direct download option:
I explain how to download, install, and use Foobar with its added ABX test component here:
My video explains from soup to nuts how to download and install Foobar and then its optional ABX Comparator component, how to take a test, and a brief discussion on how to read the final score sheet tally after finishing a test. Links discussed in it again provided here for easy access:
Once successfully downloaded and installed people can jump straight to the test taking instructions in the future, which start around 3m07s if they want. [That is, you can use it as a refresher course if you forget how to use ABX.]
There are several ways to verify the SHA-1 status of a file, if need be, but online I use the free calculator option at www.md5file.com
. Again, they may invite you to sign up but there is no need to.