Need a Better Description of How Doppler Loop Works

Doppler is more the tone / sound frequency being pushed up as things come to you and dropping down as they go away. Volume is simply a function of dissipation over distance.

Per the description in Barry's book Second Ed:

Engine must be moving to set doppler points.

Press S1 when you want it to start increasing freq coming towards you, then it passes and dopplers down in freq. as it goes away.

Note, you may not get any change in sound while setting up, the engine has no way of knowing how far you are going to stretch the doppler.

Press S2 to end the length it stretches the doppler across.

Press S3 when it's coming toward you at about half the length of the distance you ran between S1 and S2.

S4 or zero on the keypad will stop the doppler at any time.

Play with it to find what fits best on your layout.

Thanks Russell (I was looking at my printed copy of Barry's 1st book and not the electronic copy of the 2nd edition )

Well, I printed out the blurbs from the book (pages 35 and 182) and tried it and it makes less sense now.

In the SOUND MENU screen you can select DOPPLER LOOP.  Using soft keys:

S1 - marks and remembers the beginning of the Doppler Loop

S2 - marks and remembers the end of the Doppler Loop

S3 - Turns ON the sound effects

S4 - Turns OFF the sound effects

Is the DPLR button redundant or is it used for AFTER you set the initial loop parameters?  When I press S1 do I have to press the thumbwheel (same for S2)?  I did notice that when pressing S3 or S4 I didn't have to press the thumbwheel.

So, do I use the S1-S4 buttons or the DPLR button to do this?

No wonder it never seemed to work correctly for me!  I always thought that the start/stop commands were to measure the length of the loop, not the beginning spot and ending spot of where you want it to start the sequence.

To me that made more sense since the engine has to know the length of the loop.

I also thought that the ON and OFF was merely to say "I want to use Doppler now" and "OK, now I'm done using doppler so return to normal mode.".

I also thought that somehow, once the engine did the 'measure loop' that it automatically started and ended the effect on its own somehow.

can't wait to try it again.

- walt

Walt, I got it working, but it's still not what I want, can't seem to get the sounds activated when I want.

Here's a diagram of my layout:

If I'm standing at the drop-down section (where the throat of the Wye starts, at the 63" measurement shown) and want the sound to be loudest at that point and faintest in the top right-hand corner, when and which buttons should I push?

Again, when I press S1 or S2, do I have to press the thumbwheel to set the selection (the screen does not change)?  Pressing S3 or S4 automatically sets the selection I make (the screen changes).

Press S1 as the train passes the 63" point.  Wait for it to go around exactly one loop and press S2 as the train passes the 63" point again. As a practical matter, it helps to slow the engine down when pressing S1 and S2 to give better accuracy in setting the loop distance.  You can speed up the engine after pressing S1 until it comes around one loop so you don't get bored waiting; then slow it down in time to press S2.  There is a theoretical maximum loop distance you can set but your layout size should not be a problem.

To start the effect, press S3 at the 63" point (which will be the maximum volume point).  The volume will fade to nothing before it reaches the far right corner.  But when it comes around again to the 63" point it will be at its max.  It will continue this behavior once per loop until you press S4.

Now that the engine "knows" the loop distance (from using S1 and S2), you can press S3 at, say, the far right corner and that now becomes the peak volume point.  On each loop the volume will now peak at the far right corner until you press S4 to turn Doppler off.

Since the speed of sound is about 760 MPH, if the engine is running at 76 sMPH, you will hear a 10% pitch shift increase as the train approaches and a 10% pitch shift decrease as it passes.  In my opinion, the effect is best experienced with the whistle and/or bell turned on and the engine going at whatever speed limit you've established.

The way that stan2004 wrote it up is the way that I always understood it to work.  Stan2004: very clear explanation!

- walt

Of course, once you send loco a different route, all bets are off.

Bob I just push the doppler button on the bottom center row of keys on the remote. push doppler when the train is headed towards you, depending on the speed, when it gets near you blow the horn or whistle. More speed the better, over 70mph.,

Clem

Ahh.  I think Clem has identified the source of confusion. The DOPPLER (0) button at the bottom of the remote is for what MTH calls "one-time" use.  The S1,S2,S3,S4 are for setting up and operating Doppler loops to automatically repeat the effect every time the engine travels a user-settable (via S1 then S2) distance.  From the manual:

The "one time" Doppler starts and completes the effect over some fixed distance not affected by the S1/S2 settings.  I knew the magic fixed distance at one time but it's like 10 feet of track (?) - just a guess.  So if you know you want to peak the Doppler at the 63" point, there is a fixed distance of track before that point that you should hit the DOPPLER (0) button to get it to peak at 63". 

If you operate your layout from a variety of fixed locations, you will quickly compile a list of "magic" points on the layout to press the one-time Doppler (0) button to get the effect to peak in front of you.  As I recall, it doesn't matter how fast the engine is going - as long as you press the (0) button at the "magic" point it will peak in front of you.  I found this handy since you don't have to worry about how fast the engine is going - just press (0) when the train passes the pre-determined point on the layout.