keither wrote:In general, I would agree with that, however I found the output of the cheapy USB sticks distorts as the volume goes up.
It is true that cheapy USB sticks distort as the signal approaches the limits of the device. But so do cheapy mixers (think anything in the <$1000 range), and so do cheapy EQ's, and cheapy crossovers, etc.
Until a few years ago, ANY external sound card, including the $20 Turtle Beach cards, are better than (almost) all built-in sound cards in laptops. In the last couple of years, laptops have started to include 24 bit sound cards built-in...this changes the level of the playing field a little.
I use the Gigaport AG USB sound cards I bought almost 10 years ago...so quality external sound cards last a long time with even a little bit of care.
After an external sound card is added, it is likely that there is some other link in the total signal chain that is the weakest (my generic bet is on unbalanced signal connections, then mixer quality, then long speaker cable runs).
keither wrote:That distortion results in clipped peaks on the output. Those clipped peaks dump extra power into the speakers and can damage them. (Power is the area under the curve, so if you have a square wave, there's a LOT more power than under a clean sinusoid.)
Specifically, the area under a clean sine wave is 0.707 times the peak value (e.g. sqrt(2)). A proper square wave has an area of 1 times the peak value, or an increase of just over 40%.
Any music will sound worse and worse the more the signal is increased...and by the time a full square wave is achieved, the sound will be completely awful. (But I know better than to assume that anyone can actually hear that distortion AND correctly identify the cause in the middle of a gig.)
This is why every sound system should have a hard limiter setup just before the amps to ensure that no signal ever exceeds the thermal capabilities of the speaker cabinets. It might sound crappy, but at least the speakers will be protected.