Sound Distortions on Class 421 and 101

[quickthorn]

I recently bought these two items, and added AP sounds to the 4cig, but I'm noticing sound effects I don't hear in youtube vidoes of these items. I wanted to know whether what I'm hearing is "normal" or not, as this may or may not be part of other graphics/keyboard stability problems that seem to be increasing for me since RW version 7.1a (on which I'm putting together a support request for RS).

The effect is known as flanging: it's nothing to do with the wheel flanges, it's the audio effect I'm talking about. Here's a link to an example:

http://en.wikipedia.org/wiki/Flanging

More specifically, the effect sounds a bit like a "barber pole" flange or Shepard tone, like here...

http://en.wikipedia.org/wiki/Shepard_tone

...except it reverses direction over a period of a minute or so. Strictly speaking it's probably a normal flange with a very slow sweep.

I associate this with the rolling bogie sound, as it starts to come in above 20mph or so, and is worse when accelerating or decelerating. It's prominent in the cab and in outside views running alongside the moving train. With the 4cig, I sometimes get it in the cab when stationary from moving AI 4cigs. I doubt if this is how the prototype sounds, and the effect in cab is similar to a fighter jet passing at altitude on reheat, as heard from inside a large metal pipe.

I don't get these effects in core stock I had before downloading these two, and I also don't get it on the class 156 dlc I bought at the same time (although that has it's own set of issues). The 4cig is restricted to the Portsmouth route, and the effect only happens with AP sounds, but the 101 effects happen on both Ox-Pad and Newc-York. I'm not sure now, but I think the sounds were ok on the first outing or two.

I doubt if EAX is involved, as my onboard sound doesn't support that, as far as I know. I've tried the EAX tickbox, checked the sound manager and other applications, listened through headphones on a different socket and the effect has survived a cache verify. Sounds from other applications are normal.

[phat2003uk]

I know exactly what you're talking about and this effect has always been a mystery to me! It seems to happen when you have the same sound playing in multiple instances so this is why it's most noticeable with bogie run or brake rub sounds as every coach usually plays these.

[Kariban]

I think that's just one sample being slightly lower pitch than another instance of the same one ( there is some randomness you can add to the sound blueprints ). If I remember - and I can't even remember the last time I had to think about audio effects, I've not picked up a guitar in well over a decade :p it's just one waveform cancelling different parts of the other waveform out gradually as they move over each other with respect to time. If it was faster you'd probably not notice the effect, just notice the sounds were rather fuller - you definitely want it for something like multiple diesel engines, or you won't really be able to tell them apart properly ( one thing I dislike about RW3s multiple simulations is that every engine of the same type is perfectly synchronized... )

[Gatso]

This happens to all DMU's and EMU's. It also affects double headers that use the same type of loco. I've created a consist of six class 08's and the distortion is dreadful.

Some things aren't affected, these include double headers where both locos are of a different type. Class 43's/HST's are also unaffected which I guess is due to both locos being separated by eight coaches.

It would be nice if a solution can be found. I suppose with DMU's and EMU's a workaround would be to change the sound files of each coach. Perhaps even using Richard's sound pack on one coach and the default sounds on the other. With double headers you would have to clone each loco and give each clone different sounds or an AP sound pack and leave the other with the default sounds. I haven't yet tried any of these but I can't see any other way of stopping the distortion other than RSC coming up with a fix.

[Kariban]

Simple solution is to add a bit more randomness in the sound blueprint. At some point the phase shift gets fast enough that it just sounds like resonance rather than a whooshy doppler effect.

[phat2003uk]

Thanks for the tip, will try that out.

[quickthorn]

So it's not a fault with my setup as such, just an effect that arises in certain circumstances. I'm just a bit surprised it's not been brought up on the forum before, according to my searches, and that I can't hear it on youtube vids.

I can now see why certain consists suffer more, and why certain sounds generate it more. From one of the wikipedia links..

"Commonly, flanging is referred to as having a "jet plane-like" characteristic. In order for the comb filter effect to be audible, the spectral content of the program material must be full enough within the frequency range of this moving comb filter to reveal the filter’s effect. It is more apparent when it is applied to material with a rich harmonic content, and is most obvious when applied to a white noise or similar noise signal."

Some bogie run sounds are very similar to white noise, so probably explains a lot.

One DMU that doesn't seem to be as bad (from the cab anyway) is the 156, and I'd have thought that would be the worst of the lot as it's a 2 car consist made of similar units.

Thanks for the replies, very helpful.

[Kariban]

If you get two sounds with the same pitch but one started fractionally after the other, you'll get a reverb effect - and with RW starting sound instances up fast, that can often sound like you're down a pipe . What might be setup dependent is relative volumes of objects, if one is a lot louder than the other then the effect isn't going to be anything like as noticeable if you can hear it at all.

If you were a musician you'd probably be calling this "phasing", a flanger has all sorts of extra things. If you really want to see what RW is up to, make a clean sine wave sample and use that where it's going to have more than one instance.