Once you've used it some and have established confidence in the cal level, the worries subside. It would be the same as setting the mic at some random distance (which, by the way, needs cal'd too). If you don't cal the voltage, you'll still get a usable sweep response, you just won't know at what level it is. For software, it's only a relative level, but for precise external measurements it needs to be absolute.
#/TRUERTA DRIVER#
Media players, control panel, and sound card driver settings are often tweaked between RTA uses.
#/TRUERTA SOFTWARE#
When you consider the numerous software points that a sound card's level can be adjusted, it becomes clear why a known level be established. For guys like us that wonder "why", it's good piece of mind. I think you've answered my more practical concern - that the connections are indeed the same for both calibrations and that the measurements are indeed taken from the same point.Ĭlick to expand.Correct, though I consider it wise to occasionally verify it by re-running the cal procedure. If that's a known value, then couldn't the input calibration have been done automatically? Even if I'm wrong about it being a known value, surely it could be calculated because the software was told the actual voltage during output calibration and must know how much it adjusted by as a result.Īnyway, that's just me pondering the theory. 0.245 V, if the output calibration was successful? Maybe I'm throwing myself off the mark in terms of absolute values by referring to the Teac decibel tables but shouldn't it at least be some known value once the output calibration has been carried out (because otherwise I don't see what it's calibrating for)? Also, since the connections don't appear to change between the two calibration procedures (a straight line from output to input) and the measurements appear to be taken from the same point, the adjusted output voltage becomes the voltage entered for input calibration. If I'm right about it, is it not then the case that the adjusted output voltage should always be a known value, eg. If I'm totally wrong about the above, I'd love to be corrected. When you enter the real voltage, the software adjusts the output level by the voltage difference between what you measured and 0.245 V (which means there must be a direct correlation between bit levels and voltage, regardless of whether the estimated actual voltage is accurate or not) while still calling it "-10 dB" so that brings -10 dB into line with 0.245 V and all other dB levels adjust along with it, including 0 dB = 0.775 V. You then measure the actual output voltage and find, for example, that the software underestimated the sound card a bit and therefore put out a higher voltage. So, you tell the software to generate a tone at -10 dB and away it goes at what it currently thinks will produce an output voltage of 0.245 V.
According to the Teac decibel tables in my deck's service manual, that would make -10 dB = 0.245 V. My take on how the output calibration might work goes like this:Īccording to TrueRTA, they are using the fairly standard 0 dB = 0.775 V as their reference and that's good for me because so were Teac, who made my tape deck. Please advise if I should have posted in a different forum. Hopefully someone here uses it and knows what it's doing during calibration. For the output cal at least, wouldn't it be the same thing to not even connect to the Line In and just measure the voltage at the Line Out? They advise the use of a 'Y' connector to split the signal between the Line In and the voltmeter.So, are both procedures not just taking the same voltage reading and, if so, why the need to do it twice? The only difference I can see between them is they don't mention setting the input level for the output cal but, since they don't mention it, it could be set the same as it is for the input cal. For both, you connect the sound card Line Out to the sound card Line In and measure voltage while generating a 300 Hz tone at "-10 dB". I can't tell the difference between the output and input calibration procedures.My questions are about the I/O calibrations.
#/TRUERTA FREE#
I could ring the software people but I am so far using the free version and am doubtful whether they'd be willing to give phone support for that.
I'm hoping to use TrueRTA to calibrate a tape deck but have some pretty basic questions about it first and, since I get the impression a lot of folks use it to analyse speaker performance and/or tweak room acoustics, I thought I'd post this here. I'm normally over in the Tape forum and have only posted here once (I think).