To realize speaker-free speech recognition with DSP, a 2-channel recording system was developed and used to set up a speech library. The filters, including a high-pass filter, an LMS adaptive filter and a combination of these two, were adopted to separate a speaker's voice from a noisy background. The noise cancellation effectiveness of these filters was evaluated. It is worth noting that 1/f noise is shown to be a very important factor for the effectiveness of an adaptive filter. After the prior cancellation of 1/f noise at frequencies lower than 1 Hz in this study, the output signal of an adaptive filter can be improved significantly. This is of value not only for speech processing systems, but also for other adaptive filter systems.