Digital Audio provides unmatched signal security. Sixteen Bit Linear Pulse Code Modulation offers the highest level of audio performance, but uses the most bandwidth and is the most expensive digital audio system. For a premium audio service, it is still the best choice. Digital audio for video programs is best served by an inband system. Dolby Deltalink Adaptive Delta Modulation offers the best bandwidth efficiency of the companded digital systems and provides very high audio quality as well as low cost. Using Deltalink ADM, BTSC can be replaced with a secure digital transmission. QPSK modulation of the sound carrier is preferrable to in video ASK on a cost basis.