A 3D frequency versus time plot of a sweep frequency as input resulting into an measurable output is a good way of establishing the character of the echo unit under investigation. In this first example I’ve added some supported lines/comments to explain how to ‘read’ these fingerprints.
On the left axis is the frequency band and on the right axis the decay (or delay time in mS). The very first part around the 0 mS is the dry part component on it’s own as there is not yet delay added (replay heads output + dry). The gradation in color of the graph is per dB value so the curve can be translated to e.a. a filter program.
let’s have a look at some basic emulations I have here in my library:
Here, firstly, is the Meazzi model Echomatic 1’ve obtained from an eTAP2 emulation based on SPICE emulations of the original Meazzi unit’s schematics.
and here the Meazzi model Echomatic2
Now, as we’re getting more aquanted with reading the 3D graphs let’s have a look at a real Meazzi tape unit with 12ax7 tubes. I’m sure this is a surprise as the frequency bandwidth of the replay heads/tape are very narrow indeed. It’s possible that this unit was a restored unit and therefore cannot be used as a reference. I’m sure the guy owning this device feels pity for the ‘electronic’ users…should he?
Next an ‘authentic’ Meazzi Trannie. That’s not up to any standard at all! Seems hum is the main contributor. just thought of sharing this also to demonstrate the tremendeous amount of spread in the existing hardware configurations around.