The data jitter depends on more than just the crystal jitter. Using a 12 MHz crystal with a tolerance of ±0.25 % has been measured in some designs to have a jitter of -0.3 nsec to 0.2 nsec. This measurement was made with a 1.5 meter USB cable. The same design on a 5-meter USB cable has had a ±0.5 nsec jitter. AN2131 requires a clock with less than ±0.25% tolerance to meet the USB data jitter requirements.