# hdf

> import Sound.DF.Uniform.GADT

A counter is a first order `iir` at `+` with a unit delay.

> audition_text 5 (out1 (unit_delay 0.0 (iir1 0.0 (+) 1.0)))

    0: 0.000000
    1: 1.000000
    2: 2.000000
    3: 3.000000
    4: 4.000000

The graph drawing indicates two backward arcs, one introduced by
`iir1`, the other by `unit_delay`.

> draw (out1 (counter 0.0 1.0))

![](sw/hdf/Help/svg/counter.svg)

An alternative drawing can be made that includes the _read_ and
_write_ nodes that implement the recursion scheme, connected by an
_implicit_ edge.

> gr_draw' (out1 (counter 0.0 1.0))

![](sw/hdf/Help/svg/counter-gr.svg)