Posts by user "Kraftstoffvondesibel" [Posts: 38 Total up-votes: 314 Pages: 2]

I hesitate to chip in in these accident threads. Keep them clean. However, as as a few comments above brushes my audio expertise, I will comment.

A very simple audio analysis give me this:
The 3 segments horisontally, are of different videos of B787s passing overhead/landing. The vertical drop you see is the doppler effect.
In other words, these are spectrograms over time which makes these distinctions easier than a simple static spectrogram.
1. B787 landing with RAT extended.
2.Air india crash
3. B787 landing without RAT


It's a 5 minute laptop job, and it would look much prettier and clearer if I spent some time with it, (Gain to color match, and spectrally match to compensate for microphone placement and type),
but it is 85% conclusive even when done as simple as this IMO.
(I do have legal forensic audio experience)
The RAT was out judging from the audio evidence. You can see the the equally spaced overtones of the propelller match when passing overhead resulting in the Doppler effect, the difference in length of the doppler is caused by distance and the slightly varying frequencies shown in the starting point is caused by a difference in speed. But the harmonic content match.
In the 3rd segment you see none of these overtones at all.

It was hard to let it go, so I spent a bit more time with the audio, using filtering and matching to see if I could be even more sure.

It's a pity uploading audio to this site isn't as easy as uploading photos, but I can say it took very little filtering and matching to make the Air India audio become nearly indistinguishable from audio taken of B787 with known RAT extended during landing.

I can't see it in the photos either, but in these circumstances the audio is a lot more trustworthy, and from my audio point of view RAT deployment is 100% confirmed.

In the off chance that the audio I borrowed from a confirmed RAT event was somehow faked, I plotted the technical data I could find of the B787 RAT (4000rpm, 2 blades) combined with a height estimate and asked the O3 model with deep research to estimate doppler shift and speed.
The result matches the above documented 270-200Hz (in one of the harmonics) Doppler shift observed in 1.7 seconds.

It's the elephant in the room regarding the audio, isn't it, but I am not prepared to say either way. There simply is too much city background noise/ambience to discern this from the engine noise from a landing 787.

Of course one taking off would have a different signature. If anyone can point point to one taking off with the rat out we could compare.

What I find interesting is that I don’t see any evidence in the audio of the engine spooling down, which would leave a recogniseable pattern in the audio one should think. So either it is down so much that the fan rpm is down to windmilling already, or it is simply low enough in volume to be already masked by the ambience.

So taking this and moving into speculative territory for a moment, I think I read somewhere that the video with audio starts 17 seconds after the wheels left the ground.

Provided the engines were windmilling the video audio since I haven't been able to find any obvious spool down, can anyone say anything meaningful on how long it takes for the engines to spool down to windmilling rpm?

we can then backtrack from the point the video starts. How does that timing then coincide with the ADS-B data ceasing to transmit, for instance?

Putting back in the more strictly data-driven hat, I am not prepared to say so far anything about the engine working or not. You guys know more anout why the rat is out.

No, it would have looked very different in the analysis.

About the engine spool down not present in the audio:
I did not know engines spooled down that quickly if shut down in the air, I am not an aerodynamicist, but it makes sense it would happen with all the drag. I had a mental sound in my head from normal shutdowns, and action movies I guess.
That means my point about it being no spool down detectable in the audio really doesn\x92t matter.

Is there known numbers for timing RAT deployment or spool up? Because there is no sign of that either in the audio.

I will have a go at a few after take-off videos and use some alternative comparison techniques to see if I can say anything with certainty about any engine power being present or not.

My hunch, after analyzing a few landing videos with and without the RAT with the standard audio analyzers tells me the engines were at similar or below rpm/noise making level/thrust compared to a normal landing, and that they had already completely spooled down(which you guys suggest is to be expected to happen much more quickly than I thought, so maybe doesn\x92t say much) when the video with audio starts.

I don't know if anyone finds this interesting or useful, but since the questions about speed and height is coming up, based on the observer in the second video, it is what it is:

Correct. That was the original purpose of the calculation. In addition to the sound itself having the measurable harmonic signature from other rat videos.
What this plot also does however is tell you the speed if you know the height or height if you know the speed.

The iphone used to film this were pictured somewhere, knowing the iphone model, and thus the characteristics of the camera, and the dimensions of the airplane it wouldn't be impossible to calculate height from the video imo.

Just throwing it out there if anyone sees the use and feels the call.

My personal amateur speculation still centers around the cut off switches.
I have spilled coffee and sweet tea over complex electro/mechanical switches/panels before(large format audio consoles with 8000 buttons) and seen unexpected things happen.

I am sure the switches are spectacularly well built, but they are in close proximity and thus prone to the same external factors.
Does anyone know if these two cut-off switches in such close proximity has the exact same installation, or they differentiated in some way that makes a freak failure mode in one not neccesarily affect the other the same way?

I realise the discussion has largely moved on, but for completeness I have analysed, filtered and compared the audio from several 787 videos\x97both take-off and landing (the latter with and without RAT deployment; take-off footage with the RAT out is rare).

Using the same style of frequency plots employed in the RAT analysis\x97and drawing on speed of different engine components data supplied by other contributors\x97it is straightforward to identify the engines\x92 high-power acoustic signatures objectively, despite variations among clips and the presence of Doppler shift.

What is clear is that the engine noise in the recording bears no resemblance to a typical 787 take-off profile. Whether the engines were merely at very low thrust/idle or fully windmilling I cannot say with certainty, but they were certainly nowhere near take-off power.

Make of that what you will.

The audio analysis in this case isn't anything obscure or vague. The same software is used in courts all over the world every day. You can be pretty sure the same software in some iteration is used investigating CVRs all the time. It shows something emitting the exact same sonic signature as a B787 RAT went over the camera at the same speed as the Boeing 787 seen going over the camera. It isn't a broken fanblade, or a motorcycle passing by, that would give a completely different result. It literally means hundreds of thousands of datapoints fall into the exact same pattern. If it were anything else, that would be easy to observe. It is a much more accurate tool than watching heavily compressed video. It is the same software used in hollywood to surgically remove airplane noises from historical dramas, btw. At least until AI came along and took on that job about 2 years ago. . Just because you aren't familiar with it doesn't mean it isn't accurate.
Just putting this out there, since many might be unfamiliar with this, you included.

I don't believe I owe you anything, I believe this is done adequately previously and has already taken up enough time on this thread. I am of the opinion that we have shown the RAT being deployed satisfactory enough to be of use for speculation in this thread. I find repeated comments about the bad video being the only evidence a bit disrespectful, though. Even from a mere physicist. It is based on a spectrogram over time. The source file shows audio up to about 16 kHz, it is unknown whether this limitation is in the file format (ie. 32kHz sampling rate) or microphone. Doesn't matter much. The frequencies above 16kHz is not important in this context as it is not where the sound energy is anyway. The audio will have been lossy data compressed, but it does not affect these prominent properties of the audio. It does make me hesitant to draw conclusions from the parts of the spectrum with more broadband noise and several intersecting sounds. Noise floor suggests 16 bit sampling depth. Spectral resolution? N/A All samples are included. The spectrogram covers the entire frequency range recorded, It shows comparatively the same overtones of the fundamental expected from the technical specifications of the 2 bladed RAT running at it's intended RPM, the doppler characteristics fits completely with a reasonable range of passing speeds and distance to the passing source plotted out. Compareatively, All the harmonics are identical both in pitch and seperation to a recording of a known B787 landing with RAT deployed, while the Doppler fall shows a longer time frame in the landing video taken from a further distance. As expected. The overtones easily discernable in this recording falls in the 220-2700Hz range. Below that, there is other noise centered around 150Hz, which gradually fades towards the end of the recording. This, as far as I can find in available information, fits with an idling or even windmilling B787 engine, but this is not conclusive. This falls in a range of the spectrum where there are other noise sources and the signal/noise is low and of a broader band characteristic, these masking frequencies is where the lossy data compression might play tricks, so I do not weigh that heavily. Recordings of landing B787 without the RAT, shows none off the same characteristics, and completely lack the tonal components and exact overtones shown with the RAT deployed. More importantly, compared to videos of B787s taking off with normal take off thrust, the latter shows distinct tonal elements, but with very different overtones,, both in separation and composition, again possible to relate to known quantities of the rotational speed and elements of the engine at high power. The AI recording shows none of this.

The latest techniques let us separate such things as reverbration from the source, when superimposing the reverberation/ambience and background noise of the AI crash urban environment on the clean, dead open field recording of the known B787 w/rat, they do indeed sound exactly the same to this very skilled and experienced listener. Although this is not courtesy of the computer analysis. It is just another angle of confirmation.

All in all, i think this source audio is excellent. The source is an iphone, their mems based microphones, although noisy shows great spectral balance and is comparable to basic measurement microphones of professional application. There is plenty of information to analyse from in this sample.

And again, I can't see it in the video either, and until I put on some really expensive headphones and fired up the software I was of a different opinion. I bowed to the science.

Edit: I took an extra look, I am prepared to say the fall off at slightly above 16kHz is from the original recording, this is probably a limitation in the microphone, as it is not a hard cut-off before a 16kHz Nyquist frequency as it would be with a 32kHz sampling rate, there is dither noise from 16-20kHz fitting with the source being 16 bit.

Alright, just because that isn't very difficult. The first segment is a Moped/motorcycle whizzing past. Not from the same city, but it is in India, and I listened to a number of them to find a representative one, and the closest I could find in lenght/timing that isn't completely out of bounds with the streets in the area the AI video was filmed. it is taken uncompressed from a professional sound library and is a very high quality recording. The sound source is in direct line of sight, much like the AI recording when the aircraft is presumably just coming into the clear from above the roof. A moped/motorcycle in the AI video, would probably not be direct line of sight down on the street, and would have an even more ambient character, but shorter ambience. The second segment is the Air India video.
One thing we haven't discussed as a characteristic is how the AI recording moves from indirect sound with a shorter ambience, to direct sound, to a very much more ambient distant character in the same amount of time as the large aircraft moving overhead.
The moped/motorcycle in the sample, keeps about the same small street ambience throughout.
Notice how the harmonics are in different places with different spacing and with different relative intensity, the emphasis on the internal combustion engine is lower in frequency than the open Rat, but with added exhaust noise.
Thank you.



I also enclose a doppler distance

I hesitate to chip in in these accident threads. Keep them clean. However, as as a few comments above brushes my audio expertise, I will comment.

A very simple audio analysis give me this:
The 3 segments horisontally, are of different videos of B787s passing overhead/landing. The vertical drop you see is the doppler effect.
In other words, these are spectrograms over time which makes these distinctions easier than a simple static spectrogram.
1. B787 landing with RAT extended.
2.Air india crash
3. B787 landing without RAT


It's a 5 minute laptop job, and it would look much prettier and clearer if I spent some time with it, (Gain to color match, and spectrally match to compensate for microphone placement and type),
but it is 85% conclusive even when done as simple as this IMO.
(I do have legal forensic audio experience)
The RAT was out judging from the audio evidence. You can see the the equally spaced overtones of the propelller match when passing overhead resulting in the Doppler effect, the difference in length of the doppler is caused by distance and the slightly varying frequencies shown in the starting point is caused by a difference in speed. But the harmonic content match.
In the 3rd segment you see none of these overtones at all.

I hesitate to chip in in these accident threads. Keep them clean. However, as as a few comments above brushes my audio expertise, I will comment.

A very simple audio analysis give me this:
The 3 segments horisontally, are of different videos of B787s passing overhead/landing. The vertical drop you see is the doppler effect.
In other words, these are spectrograms over time which makes these distinctions easier than a simple static spectrogram.
1. B787 landing with RAT extended.
2.Air india crash
3. B787 landing without RAT


It's a 5 minute laptop job, and it would look much prettier and clearer if I spent some time with it, (Gain to color match, and spectrally match to compensate for microphone placement and type),
but it is 85% conclusive even when done as simple as this IMO.
(I do have legal forensic audio experience)
The RAT was out judging from the audio evidence. You can see the the equally spaced overtones of the propelller match when passing overhead resulting in the Doppler effect, the difference in length of the doppler is caused by distance and the slightly varying frequencies shown in the starting point is caused by a difference in speed. But the harmonic content match.
In the 3rd segment you see none of these overtones at all.

It was hard to let it go, so I spent a bit more time with the audio, using filtering and matching to see if I could be even more sure.

It's a pity uploading audio to this site isn't as easy as uploading photos, but I can say it took very little filtering and matching to make the Air India audio become nearly indistinguishable from audio taken of B787 with known RAT extended during landing.

I can't see it in the photos either, but in these circumstances the audio is a lot more trustworthy, and from my audio point of view RAT deployment is 100% confirmed.

In the off chance that the audio I borrowed from a confirmed RAT event was somehow faked, I plotted the technical data I could find of the B787 RAT (4000rpm, 2 blades) combined with a height estimate and asked the O3 model with deep research to estimate doppler shift and speed.
The result matches the above documented 270-200Hz (in one of the harmonics) Doppler shift observed in 1.7 seconds.

It's the elephant in the room regarding the audio, isn't it, but I am not prepared to say either way. There simply is too much city background noise/ambience to discern this from the engine noise from a landing 787.

Of course one taking off would have a different signature. If anyone can point point to one taking off with the rat out we could compare.

What I find interesting is that I don’t see any evidence in the audio of the engine spooling down, which would leave a recogniseable pattern in the audio one should think. So either it is down so much that the fan rpm is down to windmilling already, or it is simply low enough in volume to be already masked by the ambience.

So taking this and moving into speculative territory for a moment, I think I read somewhere that the video with audio starts 17 seconds after the wheels left the ground.

Provided the engines were windmilling the video audio since I haven't been able to find any obvious spool down, can anyone say anything meaningful on how long it takes for the engines to spool down to windmilling rpm?

we can then backtrack from the point the video starts. How does that timing then coincide with the ADS-B data ceasing to transmit, for instance?

Putting back in the more strictly data-driven hat, I am not prepared to say so far anything about the engine working or not. You guys know more anout why the rat is out.

No, it would have looked very different in the analysis.

About the engine spool down not present in the audio:
I did not know engines spooled down that quickly if shut down in the air, I am not an aerodynamicist, but it makes sense it would happen with all the drag. I had a mental sound in my head from normal shutdowns, and action movies I guess.
That means my point about it being no spool down detectable in the audio really doesn\x92t matter.

Is there known numbers for timing RAT deployment or spool up? Because there is no sign of that either in the audio.

I will have a go at a few after take-off videos and use some alternative comparison techniques to see if I can say anything with certainty about any engine power being present or not.

My hunch, after analyzing a few landing videos with and without the RAT with the standard audio analyzers tells me the engines were at similar or below rpm/noise making level/thrust compared to a normal landing, and that they had already completely spooled down(which you guys suggest is to be expected to happen much more quickly than I thought, so maybe doesn\x92t say much) when the video with audio starts.

I have seen your previous posts about this, and I happen to agree. Visually, as a lay man non visuals expert, I am in your \xabcamp.\xbb

However, the rat is small, and the artifacts are plentiful. Small sensor, compressed video, compressed upload, zoom, it is in short an awful source.

However, the RAT is a much better noisemaker, and the audio signature is much more obvious than it’s visual appearance in this case, and though the recording isn’t fantastic quality, there was more than enough information there to objectively conclude the RAT is out. And that is my professional, on the weekend, opinion.

I want to ask a pretty frank question for all of you, and I hope it is ok, from an audio specialist non-pilot:
Provided the engines spooled down. Provided the RAT is out. (There are no explosions, no bird strikes.)
Isn’t software and previous electrical failures a red herring too?Would anything but a complete fuel shut off lead to this result? That still leaves everything from the Fate is the Hunter plot, to Airbus A350 center consoles and Alaska 2059 open as root causes.

I don't know if anyone finds this interesting or useful, but since the questions about speed and height is coming up, based on the observer in the second video, it is what it is:

Correct. That was the original purpose of the calculation. In addition to the sound itself having the measurable harmonic signature from other rat videos.
What this plot also does however is tell you the speed if you know the height or height if you know the speed.

The iphone used to film this were pictured somewhere, knowing the iphone model, and thus the characteristics of the camera, and the dimensions of the airplane it wouldn't be impossible to calculate height from the video imo.

Just throwing it out there if anyone sees the use and feels the call.

My personal amateur speculation still centers around the cut off switches.
I have spilled coffee and sweet tea over complex electro/mechanical switches/panels before(large format audio consoles with 8000 buttons) and seen unexpected things happen.

I am sure the switches are spectacularly well built, but they are in close proximity and thus prone to the same external factors.
Does anyone know if these two cut-off switches in such close proximity has the exact same installation, or they differentiated in some way that makes a freak failure mode in one not neccesarily affect the other the same way?

I realise the discussion has largely moved on, but for completeness I have analysed, filtered and compared the audio from several 787 videos\x97both take-off and landing (the latter with and without RAT deployment; take-off footage with the RAT out is rare).

Using the same style of frequency plots employed in the RAT analysis\x97and drawing on speed of different engine components data supplied by other contributors\x97it is straightforward to identify the engines\x92 high-power acoustic signatures objectively, despite variations among clips and the presence of Doppler shift.

What is clear is that the engine noise in the recording bears no resemblance to a typical 787 take-off profile. Whether the engines were merely at very low thrust/idle or fully windmilling I cannot say with certainty, but they were certainly nowhere near take-off power.

Make of that what you will.

The audio analysis in this case isn't anything obscure or vague. The same software is used in courts all over the world every day. You can be pretty sure the same software in some iteration is used investigating CVRs all the time. It shows something emitting the exact same sonic signature as a B787 RAT went over the camera at the same speed as the Boeing 787 seen going over the camera. It isn't a broken fanblade, or a motorcycle passing by, that would give a completely different result. It literally means hundreds of thousands of datapoints fall into the exact same pattern. If it were anything else, that would be easy to observe. It is a much more accurate tool than watching heavily compressed video. It is the same software used in hollywood to surgically remove airplane noises from historical dramas, btw. At least until AI came along and took on that job about 2 years ago. . Just because you aren't familiar with it doesn't mean it isn't accurate.
Just putting this out there, since many might be unfamiliar with this, you included.