Downsampling, Filtering and Averaging I have a signal of bandwidth DC to ,say, 100 Hz. I am interested in the range DC-10 Hz. I oversample by a factor of, say, 30. Thus the sampling rate is 600 samples/sec. Then I bandpass filter and decimate it over a number of stages, say 3 stages (e.g. by a factors of 5, 3 and 2). Thus I get the original signal.

This gives me the advantage of having simpler anti-aliasing filter.

However, there is another advanage of oversampling, which is reducing the noise by taking an average of adjacent (extra) samples. For example, if we oversample by 4, then we take average of every 4 samples.

My questions: Do I need to do filtering before the averaging, as is the case with the downsampling?

EDITED TO CLARIFY.
Averaging is filtering with a rectangular filter kernel, which has a poor frequency response, both in pass band ripple and stop band attenuation, Because of the poor stop band response it won't anti-alias very well.  The non-flat passband will distort the final result even if there is no high-frequency spectral content to alias.