96 kHz.org
Advanced Audio Recording

Smoothed Frequency Shifting with Sub Sample Delay

For music applications with DDS or jitter compensation, it is often necessary to slightly change a frequency for some percentages. In digital domains it is not possible to resample the clock signal, because the period steps were too coarse.

This page shows a method for direct frequency tuning by adding short delays into the signal. Performing this dynamically it is possible to change a given clock frequency by only a small percentage. Sub sample periods can be added this way.

frequency tuning 96kHz by percentage

 

The example shows a circuit being appropriate for 10 MHz to by realized in PLDs like Xilinx 3020. It is possible to change the frequency in 1/16 steps. When later adding a period step delay every 1000th clock cycle, the resulting frequency was >96,0001 Hz. 

 

frequency tuning by multiplexing clocks

By switching between the delayed signals the frequency is changed slightly, which can be done in smaller steps than the period of the sample clock. 

 

 

Conclusion

Classical DDS techniques might be enhanced by dynamic smoothed frequency control.

 

 

© 2003 J.S.