Hi tophat,
Generally one would avoid doing that unless it is a last resort. 
There’s two main ways of doing sample-wise DSP in Nyquist. There’s the frustratingly awkward, difficult and slow way, and there’s the much easier and very slow way.
The slow way is by creating a DSP object. Object orientated programming in Nyquist is possible, but horrible 
There’s an example here: A Study in Pink - #4 by steve
The other way is to grab a load of samples in an array. This is made easy with snd-fetch-array (Nyquist Functions) and snd-from-array (Nyquist Functions).
One thing to be a bit careful about is that with 18 bytes per sample, a large array can be pretty heavy on ram.
An even easier (and even slower) way to access individual samples is with snd-fetch (Nyquist Functions).
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