Dynamic Noise Reduction
One of the major problems of radio systems is background hiss and noise. This is especially a problem with SCA because noise can come from the main channel, the stereo subcarrier and other subcarriers on the same transmitter. One means of reducing this noise is a system designed for long distance telephone systems called Dynamic Noise Reduction, or simply DNR.
Consider the subcarrier like a river. The bridges are the maximum volume possible and the water is noise. Everything below the water level is lost and everything higher then the bridge is cut off. With SCA the river is very high, so there is very little space for programming. Suppose we flattened or compressed our boat before sending it down the river, and then expanded it at its destination. We could send a much larger boat down the same river. It is the same with signals. If we compress the signal into a smaller package, we can send it through a noisy system and then expand it at the receiver to eliminate the noise and crosstalk normally associated with SCA.
The tiny board shown above can be plugged into the SCA-RL, SCA-RS, and the SCA-TM when utilizing the SCA-23 board. A similar board must be installed into the generator or transmitter. Be aware that DNR will not increase the range of the system. It will only reduce the noise and crosstalk.
The diagram below shows how the signal is improved.
| Signal | DNR | Noise | Crosstalk | Voice | Quality |
| Very strong | Without DNR With DNR |
None None |
Slight None |
Clean Clean |
Very Good Excellent |
| Strong | Without DNR With DNR |
Slight None |
Slight None |
Clean Clean |
Good Very Good |
| Normal | Without DNR With DNR |
Noticable None |
Masked by noise None |
Occational lost words Slight raspiness |
Acceptable Good |
| Weak | Without DNR With DNR |
Objectionable Noticable |
Masked by noise None |
Many lost words Raspiness |
Fair/poor Acceptable |
| Fringe | Without DNR With DNR |
Overwhelming Crackling |
Masked by noise Masked by noise |
Unintelligable Barely Intelligable |
Unusable Unusable |
The most important factor is that both transmitter and receiver must be modified to achieve these results. The result is worth the cost and effort.