This document presents an analysis of quantization error in FFT algorithms when the twiddle factor word length is different from the register word length. It begins with a statistical noise model to predict quantization error after multiplying two quantized signals of different precision. This model is then applied to analyze quantization error in Radix-2 and Split Radix FFT algorithms. Simulation results are presented that match the theoretical analysis, validating the model. The analysis extends previous work that assumed uniform bit widths to the more practical case of different bit widths.