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This file dates back to the year 2000. I only leave it on this site for historical purposes :)

Testing the sound output

The reason why I created the MP3 test files was the following: In the MacAmp forum, there was an argument about the volume of MALT being too high for listening to music with headphones, even at lowest system volume. Lots of people were surprised about this, because they didn't encounter this problem.
In an attempt to finally try to understand the cause of it, I created the two sine wave files, and measured the voltage of the headphone jack of my Mac (which doesn't have the problem), while playing them at maximum and minimum system volumes. The person who had this problem did the same and measured higher voltages indeed.
My test results (8100/110, OS 8.1) were:
1000 Hz:
 Max: 762 mV
 Min: 80.5 mV
 Zero: 80.5 mV
440 Hz:
 Max: 766 mV
 Min: 81.4 mV
 Zero: 81.4 mV
As you can see, even with the control strip's volume at zero, there was still sound output at the same volume as the minimum audible system volume... Weird, eh?
These values are normal, since 755 mV is a standard voltage for line out ports.
His test results (6400/200, OS 8.6a3) were:
 max: 1069 mV
 min: 120 mv
 zero: 0 mV (nothing comes out of his mac at zero)
 max: 1170 mV
 min: 120 mV
 zero: 0 mV

Note 2009/01/19: an explanation of why the lowest volume was still too loud has been lacking on this page until now. Well, better late than never: if you look at the above values, the second ones are only 3dB louder than the first ones, a small perceptual increase. But the key is within the difference between the maximum and minimum volumes. When considering what I explained about volume controls elsewhere on this site, you can see that the minimum volume in both cases is only 19dB below the maximum. Headphones with high sensitivity can probably reach at least 100dB(A) at 1100mV, meaning that the loudness at the minimum volume setting would still be a whopping 81dB(A). It seems like the volume control of those old PowerMacs is another example of an incorrect linear control that should have been logarithmic instead.

If you too find the volume of your Mac too loud, or have the same configuration (6400/200), it may be interesting to do this test.

You need: a cable which can be plugged into your Mac's headphone jack, and a multimeter or AC voltmeter (preferably digital) + the two MP3 files available on the previous page.

The test goes as follows (Important: the meter must measure in RMS voltage, normally this is the case): plug the cable in the output jack, and connect the multimeter to it (black probe to ground, red to signal). Set it to AC voltage, measuring range as low as possible within the 0-1 V range. Now set your Mac's volume to max and play each of the MP3s. Do the same with the volume at zero and at minimum audible level. That's it! You can also test if the left & right channels play at the same volume with these files and so on...
If you should get really surprising results, you can always mail them to me.

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