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Most common problems (and solutions)

The first configuration to be performed before making any test measurement concerns the audio card mixer. In the following examples a Sound Blaster SB Live! audio card is considered, but the suggestions are valid also for any other device. The operating system was Windows 2000.

1- Connect Line IN to Line OUT with a jack-jack cable and start Sample Champion. Open the Impulse Response Window.

2- Close any other software, including any taskbar application.

3- Open the internal Sample Champion mixer or the standard Windows mixer and enable ONLY the following:

PLAY Control:
- Enable Play (set level to middle)
- Enable Wave (set level to middle)
- Disable all others

Play Control settings (SB Live!)

RECORD Control:
- Enable Line-In (set level to middle)
- Disable all others

Record Control settings (SB Live!)

In Settings/General, set:
- 1 Channel In
- 1 Channel Out (16 bit)
- Buffer Length 4K
- Block = 16
- Mode = Repeat
- Sampling Rate = 48000 Hz
- Step = 4
- MLS type = 4K
- Level = 50%

4- Now press "Syncro Start/Stop MLS and Sampling" button and look at what happens.

Correct Loop-Back Impulse Response

If you will see a still Impulse Response like in the above figure, congratulations, you are lucky! Sample Champion is running correctly and your hardware/software configuration is suitable for MLS measurements. Anyway some other tests with different parameters are suggested for an extensive test.

Absence of signal Loop-Back Impulse Response

If the computed Impulse Response looks like in the above figure, it means that the chain between input and output is interrupted. Check loop-back connection and mixer settings.
The above plot can be obtained also by pressing the "Rec" button without any MLS signal in output; it is due, in this case, to the cross-correlation between the selected MLS signal (Settings/General, MLS Type) and (uncorrelated) background noise.

Most common problems:

Echo in the measured Impulse Response

If the measured Impulse Response (?!) looks like the following

Wrong Loop-Back Impulse Response

most probably the cause is in a wrong mixer setting. In the above example a repetition of the first (correct) peak can be easily observed. In this case the "Line-In" volume in the Play Control of the mixer had been erroneously enabled.

Wrong Mixer Setting

In other audio devices there are other similar level settings that must be disabled to obtain correct measurements. For example in the Pinnacle audio card mixer there is an "Input Monitor" control: set it to zero (and, if present, check also the mute button).
Obviously every "3D sound", "Reverb", "Chorus", "Spatialization" or other similar controls must be disabled for these kind of measures.

Not still Impulse Response

If the measured Impulse Response has a correct shape for a loop-back measure, but does not remain still during the cycle measures, there could be several reasons:

1- The sound card works internally at 48 kHz and emulates other sampling frequencies (this is the case, for example, of the SB Live). In this case, for MLS measurements, only 48, 24 and 12 kHz sampling frequencies must be used. Other frequencies will produce an unclean and not still Impulse Response.

2 - The sound card shares an IRQ with other devices of your system.
NOTE: this affects every audio software working in your system, so it could be worth to avoid it, even if you will not use Sample Champion.

The worst thing is IRQ sharing between audio and video devices because during sampling often graphic information are shown and this could cause problems.

This is an example of IRQ sharing (to be avoided!):

System configuration IRQ resources

As shown above, IRQ 11 is shared between Modem, SCSI adapter, USB adapters, audio card and video card!!
By the way, IRQs 2, 5, 7 and 10 are free.
The solution is to assign to the audio device one of the free IRQs. Sometimes uninstalling and reinstalling the device could be necessary, but it will be surely worth!

Following figures show in detail the settings of the audio card and of the video card.

Audio Card IRQ setting

Video Card IRQ setting

In this case Windows doesn't allow the manual configuration of the audio device IRQ and the reinstallation could be necessary. For this purpose, follow the audio device and Windows installation guides.

Other useful resources:

http://purebits.com/scfaq.html
http://purebits.com/sctips.html
http://purebits.com/appnotes.html
http://purebits.com/sckniss.html