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DCC Sound Decoders

Digital Sound Decoders put you in the engineer’s seat.








Imagine, seeing and hearing your trains as they approach . . . coming around the bend, you signal the brakeman with a long blast, then three short toots. The brakes squeal as the train slows down and comes through this tight curve. At the yard limits, signal again, then ring the bell to clear the tracks as the train enters the station. The airpumps pound out a steady beat as it comes to a stop . . . whump! whump! whump! Let off some steam and open the injector valve while the passengers disembark.

Your ears take you to another world!

While DCC has been around since the mid 90’s, the general availability of DCC sound decoders was limited (and the sounds were mostly recorded in 8bit – with many modellers complaining that these sounds were not realistic and often did not even match the sound of the locomotive). It was only around 2005 that new technologies enabled quality sounds to be recorded and stored on the decoder that the widespread adoption of sound decoders started.

Here is a short article on early Model Railway Sound Systems..

Before getting to the Manufacturers, here are some DCC Decoder Features (both sound and control) you may want to consider:

  • Back EMF
    A new motor control feature that allows for Automatic or manual Adjustments
  • Realistic Sounds
    Apart from the “normal” engine sound, more realistic sounds include the traction air compressor, the blower and others.

    • Variable air compressor sound
      Enhanced air compressor sounds on diesels so that the compressor is in sync with the RPM of the prime mover
    • Authentic braking action and synchronized sound together
      Real-life, service braking control. Apply the brake and it will prototypically slow the loco. Simultaneously, brake squeal will be activated. Stop applying the brake, or come to a stop, the squeal turns off.
    • Dynamic Braking
      Hitting Dynamic Braking not only slows the loco down, but activates the appropriate sounds. You’ll hear the cooling fans come on to cool the resistor grid, the engine notch down and the rpms drop as the train slows.
    • Synchronized Prime movers
      A GenSet Loco prototypical shuts down after five minutes. The sound of three prime movers going on one-by-one, from idle to a thundering, full-throttle rumble.
    • Stereo Sound
      If a modeler wants prototypical prime mover separation and out of sync RPMs from his dual motored E-8s, or would like one prime mover’s
      bell and horn sounds to emanate from the front speaker and the second prime mover’s sounds to come from the rear speaker, then stereo decoders may be your only option
    • Special steam sounds
      The sounds of the firebox door opening and closing, and the shoveling of coal are available. Some of our decoders even reproduce the unmistakable sounds of a spinning auger delivering coal to the firebox.
    • Whistles and Horns 
      Multiple whistles and horns have become a standard feature in many decoders.
    • 16 bit sound
      You’ll hear the difference. While some decoders still use 8 bit sound, 16 bit sound decoders which improve overall sound quality is the new standard.
    • Digital Sounds that sound like the real thing
      Decoders should deliver digital sounds that sound like the real prime movers
      Some manufacturers have sound engineers that go trackside and record each loco at its various speed notches. If the loco has eight notches, which most do, the eight notches should be recorded in sequence as the RPMs are actually increasing. Most Quality decoders should allow you to hear a diesel motor actually change pitch relative to engine speed and load.
  • Lighting control
    Decoders may offer lighting options, including gyro lights, ditch lights, mars lights, strobe lights, oscillating head lights, on-off, dynamo, Rule 17, dim-bright-off cycle, cabin lights and more.
  • Functions
    Functions deliver control/adjustments over sounds.
    In addition to the prime mover with all its associated, random sounds.
    These on-the-fly sounds include exhaust chuff, air pump, multiple coupling and uncoupling sounds, bells, cylinder cocks, steam, air and brakes, cooling fans, blower, air release, poppet valves, dynamic braking, reverse throttle, blower injector and more.
  • Noise Abatement
    Pulse Width Modulation (PWM) is typically used to control the speed of a loco. Occasionally, at low frequencies, PWM causes “noises” like humming or buzzing from loco motors.
    The latest decoders are designed to automatically eliminate the “noise” in just about all locos
  • Volume Control
    For precise volume control, many decoders feature up to 16 separate volume steps, allowing you to alter the level of most sounds separately.
  • Adjustable speed curves
    The latest decoders allow you to set your loco to react differently at every speed step. This ability lets you fine tune your loco to your specific parameters.
  • How many Sounds (Memory function)
    16Mbit memory chips are common in high-end decoders.  This allows for about 34 different horns and 14 different bell sounds on a single chip, plus multiple prime movers
  • Drop-in sound decoders
    Installation of a sound decoder should be convenient, and easy.
    Decoders should be designed to fit into your scale of choice and should take into consideration the need for speakers!


The Players:







Many modellers consider ESU to be the king of sound and will quickly tell you that the decoders are worth the premium!

ESU , a company based in Germany, launched their first sound decoders in 1999 and continues to develop new products to this day. The company offers a good selection of capable DCC sound decoders as well as related accessories.

Having worked with ESU sound decoders for many years, I may be slightly biased towards ESU , as they remain one of favorites.

There are occasionally debates about ‘which is best’ but its our experience that feature-wise there is nothing missing at all from ESU and sound quality-wise, its up there with the best of them.

The ESU line of decoders is called “LokSound”





The Technology:

The core of all LokSound decoders is an extremely capable processor, complemented by flash memory (16Mb) for sound storage, which contains the sounds, and an extremely powerful audio amplifier.

The 16MBit flash memory records up to 135 seconds of sound data, which is transferred via a polyphonic, four channel mixer with an active filter, to the last stage amplifier which is then reproduced through especially developed high-performance speakers.

Beside the actual primary sound, additional sounds, such as bell, whistle or brake squeal can be reproduced.

LokSound decoders are well known for their unique sequence-choice of the sound decoders: Steam engines, Diesel electrics, Diesel hydraulics,  Electric motors, and locos with a transmission (e.g. Rail bus, Doodlebug) can be reproduced.


  • Premium sound at a premium price
  • Excellent motor and light control.
  • The decoders are generally small enough to fit in most frames.
  • The decoder chip is programmable which makes it versatile and customizable.
  • Uses a 100 ohm speaker which limits options, but there are now 8 ohm options
  • PROS: Quality, size, design, programmable
  • The v4.0 LokSound, Select and LokPilot have really raised the bar on DCC lighting and function control.
  • The new version includes the ability to incorporate logic statements (if-then style) to control how a function responds, the ability to assign multiple effects to a single output, and excellent alternate phased lighting and control for ditch lights and strobes.
  • The latest decoder has lots of sound options, excellent features, and an overall superior design.





SoundTraxx  was one of the first companies to introduce sound decoders , which business grew out of their earlier involvement in designing computerized lighting products for the model railway market  under the name of Throttle Up! Corp.

In 1991, SoundTraxx introduced a Diesel Sound System. This was the first sound and throttle system to incorporate wireless control. This was followed a year later by the (S220-IR) Steam Sound System, the first digital sound system to offer ‘playable’ whistles.

In 1996, the company introduced the first DCC decoder to be integrated with sound and lighting (DSD-2408). Along with the introduction of the DSD-2408, came Dynamic Digital Exhaust, a method of adjusting the sound volume and ‘cutoff’ of steam exhaust chuff automatically, further enhancing the illusion of a steam locomotive ‘coasting’ into the station. In 1997, the company introduced their first decoders for the large-scale sound market with the introduction of SoundTraxx Sierra. In addition to being the first large-scale sound system with realistic lighting effects built in, Sierra was also the first sound system to incorporate a coupler-activated sound effect.

Today, the new line of Tsunami Digital Sound Decoders offers more features, sound effects and a host of other goodies to further enhance the modeling experience.


  • Excellent sound quality but the decoders also tend to cost more.
  • Excellent motor and light control.
  • A problem experienced by many modellers is heat.
  • Good Quality and design
  • Modellers have reported that Motor control and electronic chuff matching is hard to get right.







While Digitrax is probably best known for their DCC systems, the company has been producing sound decoders since first  announcing their intentions to produce a DCC sound decoder called “SoundFX” at the 2005 NMRA convention.

Originally Digitrax sound decoders were going to be available and limited to Kato locomotives only, however the company acknowledged the demand from its customer base and made the decoders available through their dealer network.

As can be expected, Digitrax offers DCC decoders that have Sound, Motor and Function either as separate or single decoder modules.






The Technology:

  • Customizable 16 Bit Sound
  • Works with SoundFX 16, 12 & 8 Bit sound files
  • 4 Simultaneous Voices
  • Downloadable Sound with Digitrax PR3 and SoundLoader 2.0 software
  • 16 Megabit Onboard Sound Memory
  • 1 Watt Sound Output
  • Cam-input-synchronized Steam-chuff option for Steam locos
  • Scaleable Speed Stabilization(BEMF) optimized for sound operation
  • SoundFX does not require an external rate sensor to vary workload.
  • 8 Ohm oval speaker on 6 Pin Plug design makes installation quick and easy


  • Early Digitrax decoders suffered from the “Digitrax Stall“- Basically, when you blow the horn, the loco slows down.  The only way to correct it is to turn off BEMF.
  • Generally, Digitrax decoders are reasonably priced, programmable, and include motor and light control.







MRC originally designed and manufactured DC train controllers and then branched into DCC.

From their first line of sound decoders for steam and diesel called “Brilliance”, the company today produces sound decoders with advanced features and most importantly decoders with great sound.


  • Compatibility with NMRA DCC standards.
  • Drop in decoders, including narrow body N scale locos
  • Mostly No wiring with easy snap-in installation
  • Wide range of decoders, including O through N scale for many popular locos
  • Sounds are recorded at trackside from working engines
  • Matched speakers


  • Good sound quality, lots of sounds in the library
  • Goofy CV logic and control design (completely non-standard), Little or no lighting options






QSI originally developed DCC sound decoders for exclusive use by BLI, and later made their decoders available to other OEM’s.

While the company does not market as agressivily as other DCC manaufacturers, they continues to develop DCC sound and control technology that is used by a number of OEM companies.

The company claims to be the owner of more DCC patents than all other manufacturers of DCC sound components combined.

QSI introduced what they termed Emulation Technology (ET™), in their Titan™ decoders. This technology models the physics of real working locomotives and using this information to reproduce the sounds coming from the model based on your  input. This means that the Titan works like an aircraft flight simulator inside, ensuring that your loco will react like a real locomotive does based on how YOU run it. QSI’s introduced the industry first stereo output (CD quality audio output, 64 channel audio processing) and new ultra-high fidelity digital sound records.

“Emulation” is a term to remember. Other sound decoders on the market produce their sounds by mimicry.

QSI’s Emulation Technology (ETTM) takes an entirely different track. Because of it, all features embedded in Titan decoders actually emulate how the prototype in real-life conditions responds to real-life conditions — and how its sounds are produced as a result.  QSI decoders sound and perform like the prototype because they think they are the prototype.

QSI decoders are HO/OO and large scale. There are no N-Scale decoders.


TCS is one of the newest DCC sound decoder manufacturers with decoders available for Z to G scale.

As the manufacturer entered the market at a late stage, their products are not as widely available. One advantage of a late market entry is that they did not have to worry about compatibility with any previous decoders and essentially looked at the market and “jumped into” the market by focusing on new technology.

An interesting differentiation is that the company decided to make all sound recordings at 24 bits and use a 16 bit DAC, and a 16 bit DSP micro controller on the decoder for what they call “superior sound”. (TCS sound files are sampled at a rate of 44,100 bit per second – better than CD quality)

The decoder has all of the basic stuff like motor control and BEMF and function mapping and such.

On the downside, it must be noted that there are only a couple of models to choose from as far as form and fit is concerned.

All decoders feature ten (10) output functions.  No need for dual decoders here but man there are a lot of wires!

There are a couple of key features that differentiate the Titan from the rest.

  • First is the level of control of all of the standard features.
    In my opinion it has too many options for most installations.
    However, if you ever wished you could tweak this or that, I think you can with this decoder.
  • Second is stereo sound.
    The Titan has introduced the ability to direct and control the placement of sound on the model.
    For a steamer that means chuffing from the front and a coal auger from the back.
    For a classic E8 that means diesel #1 plus horn and bell from the front and diesel #2 only from the back.
  • Third is the on-board sound file set.
    As I see it, you load in a complete set of sounds and then build the file to taste on the fly through a series of drop-down menus.  The selection seems fairly broad so this board covers many prototypes.  It is fully programmable so new firmware and sound files can be implemented as they become available.
  • With the release of their Emulator Technology for the Titan decoder, they have designed the firmware to “Emulate” a real locomotive.
  • It’s a real pity that the decoders are only available for HO
  • Availability remains a major issue


General Notes on DCC Sound Decoders

Sound quality of installations will vary of course, because quality of installation and quality of the sound file itself will have a very big influence on the final result, and it is also due to this reason that it is not always possible to choose a single Sound decoder Champion!

  • Sound Files

The big advancement in sound decoders is downloadable sound files.

While many off-the-shelf loco’s are supplied with per-installed sound decoders, that come per-programmed with the loco’s specific/generic sound, most high-end decoders including Digitrax and LokSound have the ability to re-program the sound files of the decoder.

What this means is that you can download the locomotive sound file that matches your loco.

If the modeler has a programmer they can change or modify the sounds in the decoder to match their requirements. A decoder that was programmed for diesel sounds could be re-programmed for a steam engine.
Many of these sound files are created by recording locomotives that are in museums. Newer models are recorded from operational locomotives.

Another area of downloadable sound files is “modified” or new sound files created by modelers.
Now a modeler can make up a sound file to match some low production locomotive that would not be feasible for the sound decoder to make.

  • Comparing Sounds

The sound that comes out of the tiny speakers in our locomotives are subject to a many variables.

* It starts with how the sound was originally recorded.
* The location of the microphone can make a big difference.
* Sound recorded with 24 bit will sound better than 8 bit recording.

Once recorded the sounds are cut up into pieces to make very small sound segments. These are used to make the sound files that are programmed into the decoders. These short segments can be less that a second to a few seconds long. Sustained sounds like a diesel idling may only be a short recording that is looped and played back continuously unit the engine speed is increased. Whistle sounds may need many parts. The startup sound, sustained sound and then the sound when you let your finger off the key.

Downloadable sounds can vary in quality and sound level. I’ve downloaded different sound files and found some to be louder. With some files you may find that one item may not sound right to you. I’ve found that the bell in a few did not sound like a US locomotive bell. Easy to try another sound file.

The installation and speaker also plays a part in the way the locomotive sounds. Last is how we remember hearing a locomotive and are own ability to hear the sounds.

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