[@gnoatto11] and [@martinoplaten13] by means of the general transform formula presented in [@grasselli13]. The resulting general model that we develop allows for the simultaneous presence of multiple stochastic volatility factors both of square root (see [@Heston93]) and 3/2 type (see [@heston97] and [@platen97]). More explicitly, the square root of each CIR factor appears in both the numerator and the denominator of the diffusion terms. Based on @martinoplaten13, we refer to this model as the 4/2 model. Our specification for the volatility process spans a large class of dynamics ranging from the 3/2 to the Heston model. This means that we can let market data dictate the relative importance of the two stochastic volatility effects that we consider. While the 4/2 model might appear as an involved choice, we will show in Subsection \[sec:unifying\] that it naturally emerges e.g. in a simple Heston setting for a suitable choice of the risk premium. Moreover, such CIR factors can be freely combined in order to drive stochastic interest rates. Therefore, the model is suitable for the valuation of long-dated FX products, for which interest rate risk becomes a relevant risk factor, see the discussions in [@gg13].\
The framework we propose is general to 