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Doppler Shift Loco Sound transmission

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Hi Guys

while waiting to move home in next couple of weeks (so I can't play trains) I've been thinking about loco sounds and how we bring it to the layout so thinking we all install our circuits and sound chips in the locos but our speaker systems can only cope with max power output say bout 2 watts so without going into the tech stuff trying to keep it simple so do you guys out there ever wonder about how to increase loco sound volume without increasing amplification in the loco ? Which because of the loco size restrictions kinda puts a damper on things and at club meetings/exhibitions we have a finite noise level governed by the speaker size and max power output ! How about if we could increase the max power output so that we could hear the loco sound above all the other noise either generally across the club room/exhibition or at a specific drivers position at the layout .

So do you think that loco sound levels could be higher on the layouts so you can hear that loco approaching or coming around the bend? Or is this a no brainier ?

Looking for some feed back !


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Hi Peadair. My tuppence worth and personal thoughts are DCC loco sound is fun and a huge improvement, but the sound that is played is 'local' or near the listener, and DCC loco sound doesn't adjust for distance (i.e. scale distance and doppler effect), or tunnels, underground, etc. Wether the loco is in a model station right in front of you or 1/4 scale mile away it sounds the same as if you are still standing beside it at the station. Technically the only way sound could adjust more realistically as a loco travels around a layout is for the player to adjust the sounds based on the two separate locations of the loco and the listener. A Dobly Digital 5.1 or 7.1 surround sound system could move the sound anywhere on the layout, but you'd need some pretty neat software to adjust and play the recordings from a layout player rather than from a loco decoder/speaker. The decoder would need to transmit fairly precise loco location data to the central system so that the receiver could simulate distance and adjust volume levels, frequencies, etc. Personally I would prefer a layout based sound technology because all the ambient noises could be added, traffic, countryside, station noises, announcements, etc, but as far as I know no such technology exists.


I the mean time I just play general ambient background railway noises from an old iPhone to a layout speaker, and a very old Hornby cassette tape copy, in conjunction with on board loco DCC sound. One thing though I have found is that I never run sound on more that one loco at a time, otherwise it just sounds like an unrealistic and confusing din. But that just my own thoughts. As a child I supplied my own ambient railway noises as mimic making all manner of machinery noises, engines, steam chuffs, rail noises, and hums with my mouth. :) Cheers. Noel

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Hi Noel

Well if it's any help I work with radio telecommunications and electronics over here so I did think maybe to experiment with sound transmission and so I do agree with what you say with regard to scale effect distance etc and although Doppler shift would not come into the equation until the final stages but I'm about to add a mini transmitter into a loco to retransmit the sound from the loco to another mini transmitter/receiver which could be placed anywhere on the layout with a range radius of about 30 metres hopefully somebody could produce a sound chip for other sound effects which could also be retransmitted over the layout while in operation and then all of the sounds come from the loco or another noise box elsewhere on the layout the idea been to put the engineer right in the middle of all the noise as opposed to standing at the side of the layout because elsewhere in the modelling world i.e. Planes boats cars trucks etc of which I'm very active in the clubs over here there are many sound chips that could be utilised by Irish rail modellers to achieve the aim.

I will keep you guys posted on what I can achieve and let you know.

CHeers for now Noel!


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Cheers Peadair. Well another option to try might be to locate a LokSound decoder on the layout and connect the speaker outputs via suitable line-in interface to a micro home stereo system, and put a LokPilot decoder in the loco, give both the same address and identical motor drive CV settings and see what happens. The sound decoder would effectively become a mere accessory decoder, but hopefully mirror what is driving the loco. This however probably will not work if LokSound uses any form of load feedback to adjust sound tracks playing (i.e. the static decoder would not be receiving any motor load parameters, current, voltage, etc). Noel

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This is going to be very difficult to replicate well, but the multiple speaker system makes sense insofar as a surround sound type effect could be created. However, the thing that seems to be missing from the equation seems to be the position of the listener(s). Right now, sound locos are not making any adjustment to even the volume alone to create any sort of scale effect sound. In other words, even in a large layout when the loco is near the engineer if might be 3-5 feet away but no more than maybe 15ft feet away when it has travelled a scale mile or two down the track. In a prototypical situation the loco might pass the observer at a hundred decibels and may be imperceptible a mile away. Most of us compensate for this by realizing that the volume on the loco's speaker is WAY too loud and is turned down to maybe 20% of its volume so that there is some fade of the sound over the limited distances on the layout.

The system would need some way of detecting where the engineer/viewer is at any any given time to even think about creating scale effect sound of doppler sound effects such as another transmitter in the cab(s) that the system can detect and react to (unless one is in a static position relative to the layout, the sweet spot, which is basically how surround sound creates its effects). Not an IT guy like some on here but these are just some thoughts.

Edited by DiveController
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Think I better have a butchers at that system and see where it leads so thanks for your info and advice and I've looked on site at that system and looks very interesting so I'll see where this takes me although I guess I'll have to do some comparisons but I should think the USA system beats my idea anytime and like I said it may just be a no brainer.


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Two seperate issues are flagged here


One is " loudness " , getting a good loud sound from a loco is a function of speaker size and speaker output power , loudness has a logarithmic square law relationship , ie 2x loudness requires 4 times the power , 4x loudness requires 100 times the power. Hence the speaker and current requirements for significantly greater loudness are considerable.


The second is the " simulation " of the both the Doppler effect and scaling up the decrease in volume to better represent a loco at a distance even though in scale terms , on most layouts the loco isn't far away at all!


Technically this could easily be done in the loco sound chip , BUT, the loco then needs to know where it is on the layout. ( or rather the dcc controller needs to be location aware )


For example , Using a combination of Railcom and section occupancy detection, it is entirely possible with current dcc systems to enable a dcc controller to issue location specific commands to a particular locos sound chip. Such commands could for example


* decrease volume as the loco moves away from the main layout viewing position

* simulate Doppler by playing sounds with rising and falling frequencies

* cut sounds , when the loco leaves the scenic area , or enters tunnels etc


Other effects could be signalled as well


* auto dimming main loco lights on entering station limits

* auto triggering flange squeal at suitable curves etc


The main impediment , besides money , is its all reasonably complex to make hang together and it's likely only a few modellers will either understand it or be bothered enough to try.


At Warley , the Belgium layout , used a combination of dcc loco sound and " layout " sound , things like proper automated station announcements etc. It was very realistic

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Just heard back from Soundtraxx in the States saying that Gaugemaster in WestSussex have their systems wherein that we can install our sound chips in there systems,so I'll be giving them a call to see if that's the case although the price of Soundtraxx is a bit steep especially when it arrives over here and Europe.


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In pre DCC days, Pacific Fast Mail did an analogue sound system, with synchronisation of the 'chuffs' coming from a cam on one of the loco axles. You had a small treble speaker in the loco and a fixed bass speaker [much bigger] under the layout. As I understand it, the principle is that the human ear can only attach direction to higher frequency sounds. Hence a mobile tweeter and a fixed woofer.

Saw the absolute ultimate in this at Utrecht back in the '90s. There was a 7mm scale American outline layout run by a German guy which comprised a station [or depot], about 30' long, which included a 13 storey tower block above the platforms. Nicely modelled too. There were just two locos - a three unit early diesel and a 4-6-6-4 'Challenger' Mallet.

It only operated for 15 minutes, on the hour, so a crowd tended to gather as per these animated clocks on churches etc. The guy appeared, magician like, from behind a curtain and the country and western music which had been playing for the previous 45 mins was replaced with the most humungous sound show & certainly one I've never seen bettered. The two locos were simply shuffled up and down the line, BUT, the 'woofers' were two 6 foot tall stacks of [very] hifi speakers, while the locos were big enough to hold decent tweeter cones.

The earth did indeed move and the diesel in particular was utterly mind blowing. After 15 mins of this, everything stopped, the C&W music came back on & the German went back behind the curtain, to do whatever it was he'd been up to with his girlfriend...

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Hornby (I think) had a system whereby an eccentric on a tender axle rubbed a bit of sandpaper onto a metal 'reed' in the tender, using the box of the tender body as a sound-board.


Quite effective for the time and the chuffs were speed-related, too, though it did compromise low-speed operation a bit.

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