Notes by ff123
This page walks you through the ABC/HR blind listening utility for Windows32 and how it is meant to be used. To get started, download this file:
64kbsPractice.zip (2.30 MB)
This file contains version 0.8c of the ABC/HR utility, a lossless decoder (flac 1.03), an mp3 encoder/decoder (Lame 3.92), an Ogg Vorbis encoder/decoder (version 1.0), and a test file (newkid.wav). When you unzip the archive, it will create files under a parent directory called "64kbsGroupTest" as follows:
In the "64kbsGroupTest" directory, there is a batch file called "encdec_newkid.bat". This batch file will decode newkid.wav (which has been losslessly compressed as newkid.flac), encode/decode the file to mp3 at 64 kbit/s, and encode/decode the file to ogg at -q 0 (about 64 kbit/s). Double click on the batch file to run and to create the wav files necessary to perform the practice run.
Now that the appropriate wav files have been created, it's time to run ABC/HR. Double click on abchr.exe from the "64kbsGroupTest" directory to execute it. The main screen with all input disabled will appear.
From the File menu, select "Open Project" and select the configuration file which has been already been set up for you called "newkid_config.txt". After the configuration file successfully opens the wav files, the appropriate portions of the dialog box will be enabled, as follows:
Notice that the play and stop buttons are enabled, as well as the portion select bar (more on that later). The ABX button is also enabled (more on that later as well). In this example, there are two active groups, labeled 1 and 2. One group represents the Lame encode and the other represents the Ogg encode. However, the groups have been randomized so you don't know whether group 1 is the Lame encode or the Ogg encode.
Inside a particular group, there are two sliders and three playback buttons. One of the playback buttons is colored blue and labeled as "Ref". This is the original, or reference file, which is unencoded. One of the other two playback buttons represent the encoded file (either Lame or Ogg), and the other represents the original. The program has randomized the order, though, so you don't know whether the button on the left or the right is the original. Play the reference file (blue playback button) to listen to the original, then play the left and right buttons within the same group.
Quick Switching: If you press a play button while a sample is already being played, the new file will switch over quickly; that is, the sample will not start playing back from the beginning. Some people like this feature, others hate it. If you don't want to use this feature, press stop before pressing another play button.
Decide which one is the encoded file (not the same as the reference). Pull the slider for this file down to rate it on the 1-5 scale The descriptions of the scale are on the far right. Don't pull a slider down if you can't really hear a difference from the original! Once you pull a slider down, the comment button for that slider will become active as follows:
Click on the comment button to write a description of what was wrong with the file that you rated less than perfect (not the same as the original). It's not necessary to enter a comment, but it's preferable.
Portion Select Bar: If you want to home in on a particular section of the sample, you can select a portion of the file using the portion select bar. Left click somewhere in the bar and then drag to select a section, as shown below:
Once you've selected a portion, you may decide that you'd like to change the starting or stopping points. You can click and drag the start and stop points of the portion you selected to change them.
Saving Results: Select "Save Test Results" from the File menu to save your results to file I suggest a filename like "newkid_results.txt". The program will reveal which sample belonged to which group, and which files you chose as being degraded from the original (hopefully you didn't choose the original!).
ABX: For encoders which vary only very subtly from the original, you might not know whether you're really hearing a difference or not. The ABX dialog box allows you to both train yourself to hear subtle defects and to eliminate the element of chance. Open the ABX dialog box and select two files to listen to. You can compare any sample against the original, or any sample against any other sample. The following screenshot shows the dialog box after you've selected two files to compare:
In this example, the original has been assigned to button A, and Sample 2 has been assigned to button B. Button X is randomly assigned to be either the original or sample 2. You decide whether X is A or X is B. Notice that you are forced to choose either A or B -- you aren't allowed to declare a tie. When you choose, the "Next Trial" button will become active and you can commit the trial. Once you commit the trial, the status boxes on the right will display the appropriate values. The "Correct Trials" and "Total Trials" boxes are self-explanatory. The "Probability You Were Guessing" box tells you how probable it is that you would have achieved those results purely by chance. The lower the number is, the better the chances are that your choices are not just by chance. Typically, you want to drive the number down below 0.05. This means that you have a 95% confidence (or greater) that your results were not by chance.
The program remembers your results as long as the session is active. You can choose to compare any other two files, then return to this comparison, and the program will re-display your progress. When you save your results to file, your ABX results, if you performed any trials, are also saved
The Progress status box is currently not implemented.
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