Actually, meditation is not associated with delta waves in the brain, but rather increased alpha and theta waves.  Delta waves are generally found in Deep sleep and have not been documented in other altered states of consciousness. There's some confusion here because some meditators have been able to scientifically prove they are consciously aware during Deep sleep, but this awareness, again, is correlated with alpha waves, which ordinarily are not present in Deep sleep.

Specially engineered audio tracks can cause changes in the brain's electrical patterns, a process called brain entrainment. These white noise tracks actually contain two slightly different frequencies that the brain translates by creating a third frequency that represents the difference between the two, the binaural beat. There's some evidence that listening to audio tracks that cause a binaural beat that can shift the brain's electrical output and encourages a different state of awareness than the usual waking state.

However, binaural beats also are not known to increase delta waves, but rather promote relaxation states that have increased alpha and theta coherence in the brain. As such, binaural beat tracks can't directly increase Deep sleep.