[sdiy] Analog Delay Lines (was) [common acronyms?]

[jhaible at t-online.de]

> Perhaps we're running with different terminologies, but I 
> believe an 
> allpass filter and the Hammond delay are fundamentally 
> different 
> beasts.
> 
> An allpass filter, one with mirror image poles and 
> zeroes, only offers 
> something approaching delay over a small frequency range. 
>  For 
> instance, the delay at the high and low extremes is zero.
> 
> But the Hammond delay is different -- it's an LC model of 
> a 
> transmission line, it doesn't have mirror image poles and 
> zeroes, and 
> it's a pretty accurate delay over a wide frequency range.

Or, in other words, it's a LPF, which has a pretty constant
delay up to its cutoff frequency, and above that, "mutes"
its output automatically with a steep amplitude slope.

JH.