The speed of a clip is the playback rate compared to the rate at which it was recorded. By default, a clip plays back at its normal, 100 percent speed. (Even if the frame rate of the source footage doesn’t match that of the sequence, the sequence automatically reconciles the difference. It plays back the clip at its proper speed.)
When you change the speed of a clip containing interlaced fields, you can adjust how Premiere Pro treats the fields. Consider making this adjustment especially when the speed drops below 100% of the original speed. (See Create interlaced or non-interlaced clips.)
You can use frame blending to smooth the appearance of a speed effect that changes the time or frame rate of a clip. To enable frame blending, choose Clip > Video Options > Frame Blend. For more information about frame blending, see Blend frames for smooth motion.