Forums

Synthesizing Engine Sounds

Started by Tim Wescott July 30, 2013
On Wed, 31 Jul 2013 10:34:52 -0500, Tim Wescott
<tim@seemywebsite.really> wrote:

>On Wed, 31 Jul 2013 04:32:29 +0000, Eric Jacobsen wrote: > >> On Tue, 30 Jul 2013 22:53:20 -0500, Tim Wescott >> <tim@seemywebsite.please> wrote: >> >>>On Tue, 30 Jul 2013 23:44:33 -0400, Randy Yates wrote: >>> >>>> radams2000@gmail.com writes: >>>> >>>>> I don't think engine sounds are purely periodic. If you synthesize a >>>>> series of sine waves locked to the tach rate it just sounds like a >>>>> tinny little buzzing sound. >>>> >>>> Wouldn't that be a function of the lowest-frequency sine wave in the >>>> series? >>>> >>>> Surely if you just keep an engine at a constant RPM its sound is >>>> periodic. >>> >>>I doubt that. There's randomness in the gasses whooshing out the >>>exhaust valves and into the intakes, and if your want to get really >>>accurate there'll be various clatters and clanks from the valve train. >>> >>>But I sincerely hope that the whooshing can be simulated by periodically >>>changing the magnitude of a random wave; I most surely do! >>> >>>-- >>>Tim Wescott Control system and signal processing consulting >>>www.wescottdesign.com >> >> I think what makes this hard is that you don't want to use a speaker or >> other audio transducer. Not sure what exactly you want to modulate to >> get the desired sound unless you really do use something like an updated >> card-in-the-spokes, like this: >> >> http://www.turbospoke.com/ >> >> It actually works pretty well: >> >> http://www.youtube.com/watch?v=iWl-aKMRq40 >> >> Not sure how you'd fit that on an electric model airplane, though, >> especially without loading it down in undesirable ways. > >Current electronic motor drives for model airplanes beep, by driving a >square wave to the motor, and using the propeller and the frame of the >plane to couple the sound to the air. > >My plan is to see what kind of quality I can get out of that. > >I also plan on getting an engine starting sound, then have it fade out as >the speed goes up. > >And, as I said at the head of the thread, there may just be too many >barriers. > >-- > >Tim Wescott >Wescott Design Services >http://www.wescottdesign.com
If you get anything working, post video or something as it'll be pretty interesting, success or not. I did something similar with a transformer a long time ago (i.e., driving it with a square wave), and discovered that the natural filtering from the inductance led to a lot of heat dissipation by the transformer. That was due to being driven continuously, but you might check that you're not adding too much heat to the motor windings during testing. I'd suspect that there's enough cooling during flight, though. I was surprised how much of the harmonic energy got turned into heat in the transformer application. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
On Tuesday, July 30, 2013 1:17:51 PM UTC-5, Tim Wescott wrote:
> I'm toying with a notion which is probably never going to come to fruition, but has me thinking hard (and having fun in the thinking). Part of it is to realistically synthesize an engine sound based on the speed of a rotating shaft. Think about a playing card in the spokes brought to the digital era. I'm pretty sure that much of an engine's exhaust note is basically an impulse or a "whoosh" of escaping gas that's filtered through the acoustics of an exhaust system. So in theory I should be able to replicate an engine's note by recording the firing of just one cylinder, then repeating this one sound as necessary, with all due overlapping as the speed increases. Does anyone happen to know if this results in a realistic sound? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Tim, Check the automotive industry. I seem to remember that a few years ago automotive engineers were looking into this very thing to generate a pseudo-engine sound for electric cars so that sightless people could hear them.
On Wed, 31 Jul 2013 09:32:07 -0700, maury wrote:

> On Tuesday, July 30, 2013 1:17:51 PM UTC-5, Tim Wescott wrote: >> I'm toying with a notion which is probably never going to come to >> fruition, but has me thinking hard (and having fun in the thinking). >> Part of it is to realistically synthesize an engine sound based on the >> speed of a rotating shaft. Think about a playing card in the spokes >> brought to the digital era. I'm pretty sure that much of an engine's >> exhaust note is basically an impulse or a "whoosh" of escaping gas >> that's filtered through the acoustics of an exhaust system. So in >> theory I should be able to replicate an engine's note by recording the >> firing of just one cylinder, then repeating this one sound as >> necessary, with all due overlapping as the speed increases. Does anyone >> happen to know if this results in a realistic sound? -- Tim Wescott >> Wescott Design Services http://www.wescottdesign.com > > Tim, > Check the automotive industry. I seem to remember that a few years ago > automotive engineers were looking into this very thing to generate a > pseudo-engine sound for electric cars so that sightless people could > hear them.
Just get Arnold Schwartzenegger to say "vroom" into a microphone, and play it back... (I used to work at a company that made telephone products. Did you know that if you call into a PBX, many of the procedural tones that you hear come from that PBX and not the phone company? I had an ambition for a while to build a system where you picked up, and got a dial tone consisting of a couple of singers singing "ahhhh" on the right notes. Then you dial. If you can't get a line out, you get a recording of some guy saying "beep beep beep...". When someone dials in, they get a recording of some guy saying "brring, brring, ...", if the phone is busy you get some guy saying "beep beep beep ..." Etc.) -- Tim Wescott Wescott Design Services http://www.wescottdesign.com

radams2000@gmail.com wrote:

> Even if you ignore clatters and random components, each individual
> cylinder does not produce the same magnitude or spectrum as any
> other cylinder, so there are components at all multiples of the
> single-cylinder firing rate as well as all multiples the fundamental rpm
> rate. This has been well-studied recently because electric cars need
> to make fake external engine noises so that innocent pedestrians
> are not run over. So you want your Prius to sound like a Porshe.
> Also the video game industry has gotten pretty sophisticated about
> making engine noises. I have seen a few papers on this and they all
> start with "periodic waveforms are not nearly good enough". There
> was an AES some years back with an entire track devoted to audio
> for games. You can probably dig up the preprints.
In real life aircraft engine sounds change a lot as a function of manifold pressure and RPM. In an aircraft with a radial engine the clanging of unsupported push rods makes the engine sound like the exhaust roar with a rattle of a metal pail of loose bolts in a relatively unloaded engine.. There are two audio filter systems in an aircraft engine intake and exhaust, both are dimensionally constant but the engine speed and manifold pressure changes resonate frequencies and harmonic content. In the air temperature of engine components are relatively constant. You might model the input and exhaust filters and simply apply a step function for each cylinder excite them tied to RPM. w..
On Fri, 02 Aug 2013 15:52:32 -0400, Walter Banks wrote:

> radams2000@gmail.com wrote: > >> Even if you ignore clatters and random components, each individual > >> cylinder does not produce the same magnitude or spectrum as any > >> other cylinder, so there are components at all multiples of the > >> single-cylinder firing rate as well as all multiples the fundamental >> rpm > >> rate. This has been well-studied recently because electric cars need > >> to make fake external engine noises so that innocent pedestrians > >> are not run over. So you want your Prius to sound like a Porshe. > >> Also the video game industry has gotten pretty sophisticated about > >> making engine noises. I have seen a few papers on this and they all > >> start with "periodic waveforms are not nearly good enough". There > >> was an AES some years back with an entire track devoted to audio > >> for games. You can probably dig up the preprints. > > In real life aircraft engine sounds change a lot as a function of > manifold pressure and RPM. In an aircraft with a radial engine the > clanging of unsupported push rods makes the engine sound like the > exhaust roar with a rattle of a metal pail of loose bolts in a > relatively unloaded engine.. > > There are two audio filter systems in an aircraft engine intake and > exhaust, both are dimensionally constant but the engine speed and > manifold pressure changes resonate frequencies and harmonic content. In > the air temperature of engine components are relatively constant. > You might model the input and exhaust filters and simply apply a step > function for each cylinder excite them tied to RPM.
I'm kinda hoping I can do that. But, to make my own job harder, the intake dimensions _do_ change on a gasoline engine as the throttle is opened -- because the throttle is opening, and presenting a larger orifice through which sound can travel. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Fri, 02 Aug 2013 15:36:35 -0500, Tim Wescott
<tim@seemywebsite.really> wrote:

>On Fri, 02 Aug 2013 15:52:32 -0400, Walter Banks wrote: > >> radams2000@gmail.com wrote: >> >>> Even if you ignore clatters and random components, each individual >> >>> cylinder does not produce the same magnitude or spectrum as any >> >>> other cylinder, so there are components at all multiples of the >> >>> single-cylinder firing rate as well as all multiples the fundamental >>> rpm >> >>> rate. This has been well-studied recently because electric cars need >> >>> to make fake external engine noises so that innocent pedestrians >> >>> are not run over. So you want your Prius to sound like a Porshe. >> >>> Also the video game industry has gotten pretty sophisticated about >> >>> making engine noises. I have seen a few papers on this and they all >> >>> start with "periodic waveforms are not nearly good enough". There >> >>> was an AES some years back with an entire track devoted to audio >> >>> for games. You can probably dig up the preprints. >> >> In real life aircraft engine sounds change a lot as a function of >> manifold pressure and RPM. In an aircraft with a radial engine the >> clanging of unsupported push rods makes the engine sound like the >> exhaust roar with a rattle of a metal pail of loose bolts in a >> relatively unloaded engine.. >> >> There are two audio filter systems in an aircraft engine intake and >> exhaust, both are dimensionally constant but the engine speed and >> manifold pressure changes resonate frequencies and harmonic content. In >> the air temperature of engine components are relatively constant. >> You might model the input and exhaust filters and simply apply a step >> function for each cylinder excite them tied to RPM. > >I'm kinda hoping I can do that. > >But, to make my own job harder, the intake dimensions _do_ change on a >gasoline engine as the throttle is opened -- because the throttle is >opening, and presenting a larger orifice through which sound can travel.
The throttle opening doesn't change the dimensions of the intake piping or manifold, though, and so doesn't drastically affect the resonance of the system. It can block and attenuate waves from getting out, and change the intake pressure on an n/a system, but it doesn't have a drastic change on the resonance. Tuners often change the length of the input piping to match the resonance with the desired peak torque rpm. It can affect the sound significantly, but so can other mundane things like the location and orientation of the air box. Throttle position doesn't affect intake dimensions, just air flow rate.
>-- > >Tim Wescott >Wescott Design Services >http://www.wescottdesign.com >
Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
>On 7/30/13 3:10 PM, Tim Wescott wrote: >> >> It's for making an electric-powered airplane sound like it has a heavy- >> metal radial engine.
Let me know if you ever figure that out. I'm sure the model airplane industry would love to know as well. Personally I think it's a crime to put and electric motor on a scale airplane. You not only want it to look real - it's got to sound real as well. I don't understand how someone can spend time building a scale aircraft and put an electric motor on it - you go to take off and all you hear is some high-pitched whine, which makes it sound like some Walmart toy. -Doug _____________________________ Posted through www.DSPRelated.com
On Tue, 06 Aug 2013 12:28:13 -0500, "DougB" <60916@dsprelated> wrote:

>>On 7/30/13 3:10 PM, Tim Wescott wrote: >>> >>> It's for making an electric-powered airplane sound like it has a heavy- >>> metal radial engine. > >Let me know if you ever figure that out. I'm sure the model airplane >industry would love to know as well. > >Personally I think it's a crime to put and electric motor on a scale >airplane. You not only want it to look real - it's got to sound real as >well. I don't understand how someone can spend time building a scale >aircraft and put an electric motor on it - you go to take off and all you >hear is some high-pitched whine, which makes it sound like some Walmart >toy.
Most of the model engines don't sound particularly real, either, especially the 2-strokes. Hard to make anything with less than 12 cylinders sound like a Merlin. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
On Tue, 06 Aug 2013 12:28:13 -0500, DougB wrote:

>>On 7/30/13 3:10 PM, Tim Wescott wrote: >>> >>> It's for making an electric-powered airplane sound like it has a >>> heavy- >>> metal radial engine. > > Let me know if you ever figure that out. I'm sure the model airplane > industry would love to know as well. > > Personally I think it's a crime to put and electric motor on a scale > airplane. You not only want it to look real - it's got to sound real as > well. I don't understand how someone can spend time building a scale > aircraft and put an electric motor on it - you go to take off and all > you hear is some high-pitched whine, which makes it sound like some > Walmart toy.
To make it sound realistic in flight would pretty much require a loudspeaker on the plane. I seem to recall seeing something like that in Flying Models. I just want something that'll raise eyebrows in the pits when I start my motor. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Tue, 06 Aug 2013 13:04:16 -0500, Tim Wescott
<tim@seemywebsite.really> wrote:

>On Tue, 06 Aug 2013 12:28:13 -0500, DougB wrote: > >>>On 7/30/13 3:10 PM, Tim Wescott wrote: >>>> >>>> It's for making an electric-powered airplane sound like it has a >>>> heavy- >>>> metal radial engine. >> >> Let me know if you ever figure that out. I'm sure the model airplane >> industry would love to know as well. >> >> Personally I think it's a crime to put and electric motor on a scale >> airplane. You not only want it to look real - it's got to sound real as >> well. I don't understand how someone can spend time building a scale >> aircraft and put an electric motor on it - you go to take off and all >> you hear is some high-pitched whine, which makes it sound like some >> Walmart toy. > >To make it sound realistic in flight would pretty much require a >loudspeaker on the plane. I seem to recall seeing something like that in >Flying Models. > >I just want something that'll raise eyebrows in the pits when I start my >motor.
It's pretty easy to rig it up to spontaneously combust. That always gets attention. ;)
>-- > >Tim Wescott >Wescott Design Services >http://www.wescottdesign.com >
Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com