Calibration of the sound card

[olflab]

Hi Guys.

I hope you can help me with your experience. I wanted to determine the frequency response of my audio interface. The result is shown here.

The Comments:
Input device: US-122 MKII / US-144 MKII
Input: 1: US-122 MKII in L
Channel: Left
Output device: US-122 MKII / US-144 MKII
Output: 1: US-122 MKII out L
Input RMS target: -18,0 dB
Actual RMS at 1 kHz: -18,0 dB
Sample rate: 48000 Hz
Clock delta: 6,7 ppm
Input volume: no control, Sweep level: -18,0 dB
20 Hz .. 20 kHz flatness: +0,0, -5,4 dB
-3 dB points: 33,0 Hz, 13,890 kHz

The upper cut-off frequency seems to be a little bit too small. The data sheet shows 20kHz for the audio interface. Is such a value realistic?

 

[DanDan]

Check your mic preferences. I believe you have selected a C weighting.

 

[olflab]

Check your mic preferences. I believe you have selected a C weighting.

It was a good tip, but it wasn't.

 

[John Mulcahy]

If you are using the Java drivers check the sample rate the card is configured at in the Windows audio properties for the input and output, if it is configured at 44.1k there will be some effect from OS resampling. Also worth testing at 96k (with the card also set for 96k in the Windows audio properties) or using ASIO drivers.

 

[Antonio Di Motta]

The frequency response curve is very different from the declared data, I saw in the Tascam user manual that the response with a sampling frequency of 48 Khz 20-20 Khz + 0.5 dB -1 dB and with 96 Khz 20- sampling 40 Khz + 0.5 dB -1.5 dB.

It is difficult to say what all this difference may depend on, in non-professional equipment the cut at high frequencies could depend on two factors: an incorrectly set anti-aliasing filter or an too high audio input capacity. I would like to exclude that this error was made on this device, when I try a sound card I loop the line In line Out on both the left and right channels with an RCA cable and then check on the PC that no type of equalizer or filter is included . Check well maybe this could be the problem also because the cut at low frequencies is quite abnormal ..
All sound cards, even the cheapest ones have a flat response up to 20Hz and I don't see why this professional card shouldn't do even better. The cheap sound cards that I use on my measurement system have a lower cutoff frequency less than 10Hz.

Regards

 

[DanDan]

Curious. The Input and Output Devices are stated as US-122 MKII / US-144 MKII
Wha.....? Which interface are you using?