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Can I take a regular plain old 1/8 male to male cable and go directly from the output of my sound card on the computer running BBP and plug it into the line in on another computer running the calibration tool? OR, is it necessary to use a resistor. I’m just confused on why it’s necessary to use the parellel port and all that stuff to create a "square wave" when BBP does it for you.
Thanks
a parallel port can produce a square wave. a soundcard output that isn’t dc straight and hasn’t been calibrated yet can’t reproduce one accurately, which is what you need to calibrate the inputs.
without a calibrated input you can’t then accurately calibrate the output with the calibration tool or use something like MPX Tool. so it’s basically used because it’s a known good source in every case so far.
Thanks very much for the response; however I’m not sure I understand. My audio input is internal and the only thing I’m trying to calibrate is the output going to the exciter. The problem is, the defaults in breakway yeilded a total lack of midrange, only a tiny bit of bass and saturated hights (crisp and crackly). Cranking up the PEQ seemed to correct this, but I had to go by ear and I’m not sure it’s spot on just yet.
My setup consists of a machine with 2 sound cards. One sound card has the stereo mix enabled to act as the internal audio input and the other sound card is the output to the exciter and runs breakaway’s compressed audio. So there’s only one output to deal with. However, I have a completely separate computer that does nothing but run the calibration tool and isn’t part of my radio station. I’m just using it as a measurement tool to fix my audio issues.
What I did is run a straight audio cable going from the analog output of the soundcard that runs my exciter (and breakaway’s audio) to the analog input of the separate machine with the calibration tool. Are you saying the input jack on the calibration tool machine will somehow skew the results?
Using this method, I was able to adjust the tilt in breakaway while monitoring the square wave in the calibration tool running on the separate computer. I then came up with a value of 88 to get an almost perfect square wave. Is this result unreliable?
Thanks again.
In order to calibrate the output, you have to calibrate the input. I must not have been clear enough about that in my last post.
quote :Are you saying the input jack on the calibration tool machine will somehow skew the results?It *can*, absolutely.
quote :Is this result unreliable?Probably. It depends on if the soundcard has a dc-straight input or not. A dc-straight input would not have a phase shift. But having a dc-straight input is almost never the case. You *need* to calibrate the input first. 🙂
Thanks very much. I undestand now. I’ll calibrate the input on my second machine with the parallel port, then calibrate the output on my main sound card.
I was able to use the parallel port to generate a square wave and calibrate my input accordingly (it was off by 2 for the tilt).
However, when I use the probe I created (with the 1 megaohm resistor) on the output to the exciter, I get strange results. Using the quicksweep wave and getting it looking like it should results in harsh, crisp highs, no mid range and a tiny bit of bass. This is after getting the tilt set correctly.
Does anyone know why this is?
are you measuring the output through the resistor?
1 megaohm is a bit huge… it might be happening if your resistor has different impedance across the spectrum. this is a common problem for headphone amps when using higher impedance headphones (250+ ohms) since the impedance changes across the spectrum on many professional "cans".
just that large amount of resistance could be making the amp in the soundcard operate that way anyways. 10,000 ohms is standard for a line level input. so adding a million more does seem a bit excessive, no?
I am measuring the output through the resistor. The 1 megaohm resistor does seem excessive; I just used it because that’s the resistance the calibration tool called for. However, if you think it would help I’ll try the 250 kohm one.
Alcyone, the level of resistor is a bit subjective, a 1meg can result in a very low level and a noisy squarewave, I personally use a 100k and this seems to cover most cards fine, I have occasionally bypassed the resistor totally for a very insensitive card but in most cases some kind of resistor is recommended.
I used a 100 kohm resistor and got what I believe to be more accurate results. I think I’ve got the tilt set correctly now, but when I get the quick sweep wave looking like it should, it results in distorted highs and no mids or lows. Do I need an oscilloscope for this?
You might need a scope for it. That’s one thing the calibration tool can’t show you… is if your audio INPUT used in this process actually has proper frequency response. If the soundcard you’re using for input isn’t flat (only tilted is ok since that can be fixed) then you obviously can’t tune the frequency response of the output either. Rose colored glasses, as the saying goes.
It’s not a bad idea to have a scope around anyways, since you can get them on eBay for under $50 USD.
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