What are the disadvantages of Digital Signal Processing?

There can be few ,

1. Speed & the Cost

DSP Design cost can be very expensive when large bandwidth signals are involved . Even the ADC ( Analog to Digital Converter ) and DAC ( Digital to Analog Converter ) device prices are high for large BW scenarios .

Speed is another concern . Currently DSP devices are not faster enough to cater all the requirements in the world of signal processing . At the moment only up to moderate BW Signals can be processed . Bandwidths are in the 100MHz range are still being processed by analog methods since the DSP methods available are not faster enough .

2. Design Time

DSP Design time may be too long . And for DSP design, you should have a skilled, and perfect people who knows well about the DSP techniques . Also you should have the required toolset, specially the required software packages . Without these the DSP sometimes be impossible .