TuneLab users: If any of you use the sound generation feature of TuneLab there is a small chance that your computer may not be producing a calibrated pitch when used in this mode. This finding does not affect the calibration when used in normal "listen" mode - only when producing sound in your computer's speakers. Background: The sound system in a computer is generally capable of both producing sound and listening to sound. When TuneLab is calibrated for pitch, the exact sample rate of the "listening" system is determined for your computer. This exact sample rate is involved in all subsequent pitch calculations. When TuneLab generates sound, it assumes that the sound output sample rate is equal to the sound input sample rate. In most computers this appears to be true. But I have found at least one desktop computer with a soundcard that has independent sample rates for sound input and output. On this particular computer, when I calibrate the input system to a precise external reference tone and then switch over from listening to producing sound, the generated sound appears off by 12 cents. You can check the calibration of generated tones with nothing more than a tuning fork. In the listen mode, adjust the offset of TuneLab until the boxes are stopped for the tuning fork. Then switch over to generating sound and listen for a beat between the tuning fork and the tone generated by TuneLab. There should be no beat. -Robert Scott Real-Time Specialties (author of TuneLab)
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