We present an algorithm for design of a joint source-channel coder using a channel-optimized quantizer and multicarrier modulation. By changing the power of each subchannel in the multicarrier modulation system, different error protection can be provided for different bits according to their importance. The algorithm converges to a locally optimum system design. Compared to a Lloyd-Max (1982, 1960) scalar quantizer or a LBG vector quantizer using single-channel transmission, our optimized system can yield substantial performance improvements. The performance improvements are most pronounced at low channel signal-to-noise ratios.