In a transmission system for digital symbols, such as used for DVB, source symbols are encoded by a block coder (4), subjected to an interleaving operation in an interleaver and subsequently encoder in a channel encoder (8) according to one out of a plurality of possible channel codes. The output symbols of the channel encoder (8) are applied to transmit means (10). These output symbols are modulated on a carrier and applied to an antenna (12). An antenna (14) connected to a receiver (16) receives the signal transmitted by the antenna (12). Receive means (18) are arranged for amplifying and demodulating the signal received from the antenna (14). The output of the receive means (18) are applied to quantizing means (20) which convert its input signal into a quantized digital signal, before applying it to a Viterbi decoder 22. The complexity of the Viterbi decoder 22 depends on the number of quantization levels at the output of the quantization means (20). Consequently, this number of quantization levels should be not too high. On the other hand a too low number of quantization levels results in a degradation of the performance of the Viterbi detector (22). A suitable choice of the quantization levels depends also on the channel code used. According to the inventive concept of the present invention, the quantization levels are chosen in dependence on the channel code used. This channel code can be represented by the puncturing rate. In a preferred embodiment the quantization means are realized by a cascade connection of an analog to digital converter (34) and translation means (36). The translation means (36) converts the constant quantization levels at the output of the analog to digital converter (34) into quantization levels which depend on the working point of the channel code used.