- Introduction |
- Hardware |
- Software |
- Sound Quality |
- Reference |
- Enjoy
An introduction to computer audio
- Amplifier
- ASIO driver
- Audio cables
- Bit perfect jitter
- Bits: 16 or 24
- Clock
- Crossover
- CDtext
- CDP vs DAP
- Cue sheet
- DAC
- Digital cable
- Direct Sound
- DLNA
- Driver
- DSP
- FireWire
- Headphone listening
- Hearing
- I2S
- ID3
- Kernel Streaming
- Memory player
- Music Server
- Perception
- Performance
- RAID
- Ripping
- RFI
- Router
- Sampling, up and over
- Sample Rate Conversion
- S/PDIF
- Tagging
- Toslink
- Transcoding
- Units
- UPnP
- USB
- VST
- WASAPI
- WAV
- Wave Out
Believing is hearing
It might be interesting to read a primer about perception. These psychologists do all kind of very funny experiments.
As usual you have an experimental group and a control group.
You give a paper on digital audio to the experimental group and ask them to rate this paper (hopefully not this one). But before you do you tell them a little more about the author. Now this turned out to be one of the founding fathers of digital audio, key role in developing the CD, an highly respected expert in this area, etc, etc.
The control group is asked to rate this paper but you won't tell them any thing about the author. Guess what, the experimental group rates this article significantly higher than the control group.
Like wise, give both groups exactly the same text and ask them to rate it. The only difference is, at the bottom of this text there is a name, in one group this name indicates it has been written by a man, in the other group by a woman. Guess what, there is a significant difference in rating and any woman can tell you which one was the lowest.
What we belief, we will hear. What we don't believe, we won't hear. That’s the difference between an audiophile and a skeptic.
ABX
The best way to protect yourself against your own believes is to do a ABX test.
You have bought a high end power cord.
Listen to your equipment with the standard power cord, call this A.
Listen to your equipment with the high end power cord, call this B.
Now you know exactly how A and B sound.
Now ask a friend to do the X, he will connect a power cord at random and keep notes (trial 1=A, trial 2=A, trial 3=B, etc.)
You don't even want to know which one he is using, you are a scientist, you want to establish facts not prejudices. Your keep your notes.
After 16 trials, you compare notes.
If you are above change level, you can hear the differences, you have made the right choice.
If you are not, you know you better don't spend your money on another high end power cord. You win anyway.
An ABX test removes the bias of the listener.
No more, no less.
If the score proves you can identify A and B correctly, well you haven proven that you can hear the difference. Not to be mistaken for A sound better than B, that’s a judgment.
The ABX method is about perceptible differences, not about quality.
If you don’t hear a difference, well you don’t. You have not proven that there is no difference. You have proven that you in this specific experimental setup are not able to discern between the two. A different setup or another person might yield different results.
A good example of a blind test in practice, comparing speaker cables.
I admire the courage and the honesty of the poster, Mike Lavigne.
People able to admit that they spend over $ 30.000 (thirty thousand) on a speaker wire for zero audible difference are rare.
More about ABX: http://www.hydrogenaudio.org/forums/index.php?showtopic=16295
Dated but a good read: ABX Double Blind Comparator
If an ABX test shows a statistically significant difference then you can reasonably conclude that there is a difference. Unfortunately, a likely outcome will be that the test will not show a statistically significant difference. In that event it would be improper to conclude that there is no difference. You will be back where you started.
Absence of evidence is not evidence of absence.
Tony Lauck
ABC/HR
ABC/Hidden Reference ( ITU-R BS.1116-1) is pretty much like ABX.
This time the listener also rates the difference on a standardized score.
This method allows for qualifying the difference.
It is a recommended method for testing for small differences between codecs and the original.
More: http://wiki.hydrogenaudio.org/index.php?title=ABC/HR
MUSHRA
MUlti Stimulus test with Hidden Reference and Anchors is recommended for audio quality assessment by EBU/ITU-R.
The MUSHRA approach is recommended when there are obvious differences between codecs and original, but small differences between codecs tested.
The listener is presented with the reference (labeled as such), a certain number of test samples, a hidden version of the reference and one or more anchors. The recommendation specifies that one anchor must be a 3.5 kHz low-pass version of the reference. The purpose of the anchor(s) is to make the scale be closer to an "absolute scale", making sure that minor artifacts are not rated as having very bad quality.
It is used to compare lossy codecs.
More: http://www.ebu.ch/en/technical/trev/trev_283-kozamernik.pdf
Experimental setup
All these testing methods have one thing in common, removing the bias of the participant. They won’t prevent you against errors in your experimental setup.
If in an ABX test you hear a significant difference between Toslink and USB it might be because Toslink is set to full range, USB to laptop speakers. If you overlook these kind of things you come to the wrong conclusion using the right method.
How long should you listen?
Much to my surprise, sometimes very short.
Tomasz, regarding memory-based testing and instant switching:
Such things are determined by the test interface, not necessarily the test procedure. In my opinion, an interface which does not allow the listener to define playback loops of arbitrary length (down to 1 sec or so) or to switch between codecs during playback (maybe with some short crossfading or fade-out and fade-in to prevent clicks) is a bad interface. Regardless of whether it's an ABX, ABX/HR, or MUSHRA test. For me, personally, loops of 2 - 3 sec reduce bias due to my memory to a minimum. Indeed, if I make the loops longer, I start to forget the "sound details" of the beginning of the loop when I reach its end, and that makes it difficult to compare two loops. I usually don't go lower than 2 sec, though, because then the looped segment loses stationarity, and I run into the risk of focusing more on loop effects than on the recording itself. But these numbers vary somewhat from person to person.
C.R.Helmrich
Loudness matching
Loudness matching is very important when comparing products because the perception of timbre, spatial and dynamic attributes are level dependent.
A lot of sales man know this. Just turn up the volume a little when demonstrating the expensive one does wonders.
Listening position
An important aspect is your seating position.
You listen to your system.
You swap a speaker cable and start listening again.
You do hear a difference.
Your conclusion: you do hear differences between speaker cables.
Another conclusion might be that you do hear a difference because your seating position has changed. In fact, a shift of just 4 inches makes a difference. Not a ‘audiophile’ difference but a measurable difference.
Frequency response at two locations four inches apart
Ethan Winer: Why We Believe. A common-sense explanation of audiophile beliefs.