The sound of metal being struck like a bell or tines of an electric piano. These sounds contain complex harmonics that are difficult to achieve any other way. Yamaha's DX range of synthesizers are FM synthesizers.FM synthesis modulates one oscillators frequency with another. Bit like pitch modulation with an lfo but using a hfo instead. Multiply that by 6 and you have a DX7. Btw all oscillators on the DX7 are sine waves onlyI don't know what you mean by metallic sound
Blofeld is a wavetable synthesizer. This has many digital soundwaves including lots of FM type waves for creating the same kinds of sounds.
Both these options are at the cheaper end of the scale. There are many other similar synths out there that can do similar.