Q: Program does not work; it produces some error message like "Cannot open input/output sound device"
A: Make sure your sound card driver is installed properly. Also make sure that your sound card is full-duplex, and full-duplex mode is supported by the driver.
Another reason may be that your sound card does not support the default sampling parameters of 44100 Hz/16bit/mono (which is possible only for ancient sound cards :-) Press "STOP" button, go to menu -> Options, open the options dialog and try to set different parameters.

Q: It seems GNUitar works, but I can't hear effects applied to my guitar sound. "Clean" sound of the guitar is send to the speakers, but with no applied effects. I hear native noise of effects, and it seems like there is zero input signal send to effects.
A: Make sure your line input or microphone input levels are not zero. Use your OS mixer program to adjust input levels.

Q: I hear both clean and processed signal in the speakers.
A: Press "mute" checkbox on the line input channel in your mixer program to suppress clean sound.

Q: GNUitar noises terribly !
Q: The output signal is over-amplified/distorted !
A: The trick is with the levels of signal. You should adjust your mixer properly. Set the line input to maximum level, wave out and master volume to middle level, and then start to decrease master volume until the noise will become minimal. Increase volume on your external amplifier.
The reason of problem is that some soundcards have poor signal/noise ratio in full-duplex mode. To eliminate noise, you may do the following:

• use protected cable to connect guitar into the PC;
• ground your PC properly;
• there is a possible noisy card (video/modem/LAN) on the motherboard next to your soundcard. Try to move sound card as far as possible from it.
• try to use high quality low-noise pre-amplifier BETWEEN your guitar and PC. Please be extremely careful with the volume control of your pre-amp -- the sound card can be damaged if you set loud volume on the pre-amp. The main goal of pre-amplifier is to decrease signal/noise ratio between the signal will be passed to sound card. Please understand that the program processes both signal and noise, and the noise in the output is just the input noise amplified and distorted by effects.
• use the effect "sustain" as a pre-amp. Set "Gate" and "Sustain" parameters to 100%.

Q: The latency is poor. Is there a way to improve it ?
Q: How do I fight the buffer overruns ?
Q: How do I achieve the best performance ?
A:

• The lower is the sampling rate, the better is the latency. Drawback is the sound quality.
• The lower is the fragment size, the better is the latency. Drawback is the higher system load.
• The hearable periodic scratches (DirectSound output) can be fixed by decreasing the overrun threshold (sampling params dialog).
• Increase the fragment size and decrease the sampling rate on low-end CPU, to gain the best latency/overruns/load ratio.
• On Windows, prefer WDM drivers, if possible. Try both MME and DirectSound playback; choose which is the best.
• Prefer Linux over Windows. Properly tuned Linux kernel has 10-100 times better latency on the same hardware.
• Make gnuitar executable setuid root on UNIX, to allow it run with increased priority.