Soundcard Calibration Check

[Hipper]

Greetings All.

I have a laptop with Vista Basic and an Audio Advantage Roadie external soundcard. I was told this soundcard is identical to the recommended AA SRM (except it is a light grey in colour) and with the Vista drivers, should work the same.

I've completed the soundcard calibration and got what appears to be an acceptable result, although not as good as the SRM graph on the 'Vista Soundcard' page, notably in the high frequencies. Incidentally I have tried different cables and Sweep Level dB settings (-6 to -12). The cables made no difference but the dB settings flattened it slightly on occasions.

I then proceeded to check the calibration as per instructions and get the resulting graph (sized for the lines to fit on the picture):




The dotted line is the sound card calibration, the straight turquoise line the Filters 0.0dB, and the blue line 'Corrected' at 74.7dB.. This latter seems to be roughly the inverse of the soundcard line.

What is happening here and where is, if it exists, the actual result of the check as per the help pages?

Please excuse my ignorance!

[JohnM]

The "corrected" trace is actually a dotted blue line underneath the solid blue line which is your measurement. The soundcard cal looks a bit noisy and seems to roll off quite early at the top end, but would need to see the vertical axis zoomed out to span a few dB to see what the actual shape is. Make sure you do not have a wireless card active while making your soundcard cal or other measurements as that can result in glitches in the captured audio.

[Hipper]

Thanks for the reply.

Here are some more images of the graph of the soundcard calibration:





There's certainly a lot of wiggling going on around 20kHz (although I can't hear at this frequency anyway).

I'm new to laptops and Vista but I did check everything before starting: closed down all security (I'm not on the internet with the laptop), wireless card and anything else I could find. The Roadie is the default soundcard and it works (I've used the line-out to play speakers). I've connected at the USB end with stereo line in and line out loop (3.5mm stereo connections). I've followed the exact arrangements described on the Vista Card thread in the Roadie Control Panel, in terms of volume control (Playback Line In and Microphone muted), speaker set up (2 Speakers, Eq and Effects off) etc.. The Roadie flashes as the measurements are taken indicating it is getting a signal. I must say that the volume controls are set very low, both line-in (Record Settings) and Master, in order to get the signal to -12dB.

This is as far as I've got with REW. I haven't done level checks, SPL calibration etc..

[brucek]

I don't think the calibration file is especially bad. It is a bit challenged at the top end, but so is the SRM that it supposedly is a proxy for....

If you examine the original graph you posted with the blue loopback response gyrating around, it isn't such a bad thing since the vertical scale divisions are a exaggerated 0.2dB per division. Either way, I don't think I'd use your soundcard for measurements above ~15KHz.

brucek

[Hipper]

Many thanks.

I suppose it's too easy to get bogged down in details like this! As you say, the soundcard calibration is not really so bad being at most 0.15dB out until below 10kHz.

I've found (at 55 years of age) that I can't hear anything above 12.5kHz and at the moment I use a Behringer DEQ2496 Digital Equalizer in my Hi-Fi and have started the high end roll off at 12.5 kHz down to -15dB at 20kHz and it made no difference to the music for me.

There's still something I don't understand though: why don't I get a straight horizontal line after doing the soundcard calibration check? That's suppopsed to be no more then 0.1dB off I thought.

Thanks again.

[brucek]

why don't I get a straight horizontal line after doing the soundcard calibration check? That's suppopsed to be no more then 0.1dB off I thought.

I would suggest the problem is how rapidly the response changes where the flat line measure starts to misbehave. Up to that point the flat line loopback is well within spec.

Normally a response quietly trails off, lower and lower, and REW can follow along and compensate quite nicely. Your response at the top end is more of an oscillation.

You can play with the sweep level of the soundcard cal routine and try and smooth that upper grsph somewhat and the REW would behave a bit better at the top end. Certainly if you're using REW for subwoofer measurements (the usual around here), the soundcard cal file you have would be perfect.

brucek