Help with ambient sound capture Mic

M

Matheus Jardim

New member
Hello.

I`m veeery new on this subject and I would like to know if anyone could help me choosing a Microphone for ambient sound acquiring.

We aim to use this Mic for acquire a Motor sound of a car running but we would like to get minimal interference of other sounds. which tipe do you guys think is the best?

Can anyone help me with this?

Thanks
 
Is it really "ambient" if you're trying to capture one specific sound?

Is this to be done while the car is rolling down the road, like from a distance as it drives by, or are you going to somehow attach the microphone so it records a long sequence, like with the car accelerating, shifting gears, etc? Obviously, the latter would require some kind of rig attached to the car that could move along with the car, as well as have some protection from the stray junebug, gravel or other hazards.

Regardless, I'd think any decent dynamic mic with a cardioid pattern like the SM57 should be fine, assuming you've got a mobile recorder that you can plug it into. Otherwise, just get a portable digital recorder.

What's the rest of your recording setup look like?
 
Hi Keith! Thank you for your reply.

So the ideia is to acquire all the sound that the motor goes by, such as accelerating, shifting and etc; so we`ll need to keep recording as the car is rolling.

I havent put much effort into the rest of the recording setup for i am very new into this, so if you would give me a hand about that too, I would be very thankfull xD!

So the ideia is to extract the Mic response (in Intensity or Db) and use this sound spectrum into some sound editting program too understand a little but about how`s the motor sound response from the start of it to the end of a trip.

Sorry if its too much, hope you could give me a hand!

Thanks
 
What is it for?
You have a number of options. You could do a stereo recording that would capture the 'real' sound of the vehicle passing left to right - The success of this depends on how far apart the end loudspeakers are. The impact of course lessens as the speakers get closer together and the other problem can be that if you are trying to match sound and pictures then the speed of the effects needs to match the vision.

You can also use much tighter, mono directional microphones and record in mono and then turn this into pseudo stereo in the edit. Very often newcomers are very disappointed by location recording of things like cars - because a car accelerating and gear changing needs a really quiet and open enforcement and once they are on their way, the volume level goes down and the noise from people, things and wind get in the way. Outside, wind can be a real killer - so some form of wind proofing is needed.

I'm sure we can all help - but we need you to explain in much greater detail what you have in mind, where you want to do not and and what kit or equipment you already have.

Things to remember are that realism is a proper question. Do you want the real sound of the car passing or the sound that people would believe is the car passing. Think of all those American shows where every car squeals going around corners - which in real life they don't.

As Keith said - a single SM57 would record a car passing in mono, or two of them could do a reasonable stereo recording. If you are green to the recording techniques you'll need, you might need to do some swatting up.
 
Ok! thanks for the reply! i'll try to explain as detailed as i can.

So the ideia is this: We want to record the sound response of the motor from a constant point (the ideia is not to change the distance from the mic to the motor never) so in the end of, lets say, a week; we have an ideia of the sound response that the motor makes in different tasks.

With this sound response we will create a statistical model of response of a ''Healty motor''. The ideia from here is to keep monitoring the sound of the motor, and if differs from the model of a healty motor response, we would know using control charts (another statistical tool).

So I think the main issue with this is: Which setup i have to use to achieve this study (I know the statistical part of it, but i have 0 knowlegde of the sound setup needed for this study). I would need acess to the Mic output (in Hz, dB or any other format) constantly, so we can monitor in real time.

So the main issues in my head are: We need to capture the motor sound as the major response, so outside influence sound would not be very good for this study (as it influences the statiscal model in a bad way) and we would need to monitor the sound response continuously for a long period of time (several months).

Is this detailed enough? As i said, i have 0 knowlegde of this, so feel free to ask me any info you need.

Thank you so much guys, you are really helping me with this.
 
Oh boy, that's a complicated thing you are describing, but I don't think a single microphone would work. Just lift the hood of a car while it's running and stand on one side and then the other - you've got different belts, pulleys, alternator, AC compressor, etc. all over the place. A minimum of 2 mics under the hood if you're really trying to capture the engine sounds, probably more like 4 or more, honestly. Just a single microphone is going to be overwhelmed by the nearest sounds IMO, even if you put something like a boundary/omni attached to the hood of the car, it's going to basically be hearing just top-end and injector noises (e.g.).

And, I doubt any microphone would be recording the same thing (if anything) at the end of a month in that environment if you ignored it. If it hadn't been rattled to the point of failure, it would probably be clogged up from the fine bit of dust and petroleum vapors present. At the very least, you'd need shock mounting and a kind of (easily) replaceable filter to protect the microphones, with some kind of routine maintenance program to check on them. Then, I think you'd have to set up a dedicated recording device with tons of storage - this might be a good Raspberry Pi project, honestly, because digital recorders are limited to SD card storage, and you'd fill those up in a day probably, maybe longer if you record at low bitrate MP3, which might be good enough, and tucking a PC in the trunk seems like overkill for something single purpose, but maybe a Linux box with a massive SSD would be good for long term.

Sounds interesting, but maybe a little more challenging than what you were imagining.
 
Hummm i feel you, still i think we can make it work, since we wont be needing to store the data in the monitoring process, the data is processed then discarted.

Since we are prototyping it, the ideia is to use a motor outside the car maybe. We can ran a motor in our garage, so in a control environment and just capture the sound of it working. In this setup what kind of Mic and other equipments do you think i`ll be needing? the ideia in this cenario is to focus on acquiring the sound of the motor.

Thank again! wait for your reply if possible.
 
Matheus Jardim said:
Hummm i feel you, still i think we can make it work, since we wont be needing to store the data in the monitoring process, the data is processed then discarted.

Since we are prototyping it, the ideia is to use a motor outside the car maybe. We can ran a motor in our garage, so in a control environment and just capture the sound of it working. In this setup what kind of Mic and other equipments do you think i`ll be needing? the ideia in this cenario is to focus on acquiring the sound of the motor.

Thank again! wait for your reply if possible.
Click to expand...
How are you processing and then discarding the data? What does that?

If you want "the sound of the motor" (however you define it) you need to tell us what kind of processing you plan to do, i.e., what form must the data take in order to be useful?

If all you want is to see the waveform go by on an analog scope, then plug whatever that device needs into it, and set up your movie camera I suppose.

If you want an audio file that you can play back on a computer, then you can stick a digital recorder of any kind on a stick/mic/camera-stand in front of the motor, press RECORD, and let it write digitized audio files to the SD card, which you can copy to a PC for analysis or simple audio playback.

P.S. This is also a place where a "USB microphone" might be a relatively simple solution. Plug one into a computer and let it record until you press Stop.
 
Hi Matheus and welcome. Now I guess the guys here get fed up with me saying this but! Ask as well at Sound On Sound | The World's Premier Music Recording Technology Magazine
I would be very surprised if someone there has not at some point in their professinal lives done something similar.

My thought are: you are actually collecting "data" albeit in the form of sound? This has two consequences in my mind.

1) The microphone needs to be as flat in its frequency response* as possible. That implies some form of measurement mic. Not cheap.
2) Calibration. You need the sound levels being recorded tied to a known SPL at a consistant distance fron the engine. For that you need a Sound Level Meter. These come with different "weightings" responses. A and C being the most common and which scale you use very much depends upon the end point use of the data. For example, for music purposes, studio monitors, the C weighting is used. Noise test, roads e.g. uses A.

I don't think this will be done at all well for monkey food!

I don't know about the other guys that have responded but I still have little idea of your intended setup and MO? A rough drawing mayhap?

*This is again dependant on purpose. Are you for instance only interested in the nominal 20-20kHz audio range or do you need to go outside human limits?

Dave.
 
Thank you for the reply.

I`ll try to explain a little bit better the output of the sound i need. I dont know if it`s possible, but ideally we would need: Intensity of the sound (maybe dB) x Frequency in .txt or xls. and Also we would need to monotoring this over time; so in the end we would have a sheet thats Intensity x Frenquency and over time.

So the setup would have to be able to give me this information in order for me to generate a monitoring model or i would have to have a way to extract that information from our files.

In a simplier setup, i could just have the Intensity of sound (dB maybe) x time ;

I`m sorry if I`m not beeing so clear about the project, but i`m trying to explain the best way I can.

Please, fell free to ask more questions.

Wait for your reply
 
Hey Dave! thanks for the reply.

So i think i explained myself a little bit better just a minute ago hehe, havent seen your reply.

could you please check my reply to see if it helps?

Thanks!
 
Matheus Jardim said:
Hey Dave! thanks for the reply.

So i think i explained myself a little bit better just a minute ago hehe, havent seen your reply.

could you please check my reply to see if it helps?

Thanks!
Click to expand...

Not really (but then I am old, dim, medded up and just recovering from a cold) Now...PLEASE do not take this as a slight, in most instances it would not matter but.,,You REALLY need to get a good book about acoustics and recording because you have used terms in slightly incorrect way and since (it seems to me) this is a serious engineering/scientific project you need to have and understand the right words.

"Intensity" of sound is in fact more or less equivalent to "power" (in watts) and is not how we experience "loudness". We are sensitive to sound pressure and that is measured in decibels.

I am sorry to pull you up like this and yes! Pedantic IF you like but it seems to me you have a lot of work ahead of you and IMHO you need to get some basic acoustic/electro-acoustic terms well understood? Otherwise this could I feel undermine the whole validity of the exercise.

AND!! Before you ask! I am NOT the guy to help you with such learning. My knowledge is very limited, patchy and specific to what I have NEEDED to learn at a particular time and is now mostly forgotten.

Dave.
 
Hi Dave!

In any way i feel bad about your comments. I am in fact a chemist and my part is the statistical analisys and chemometrics, so acoustic is not my area. And you are right, i should start learning (and i intend to) do it. I have a team to help me with, and i know that thats not an easy project.

I did, in fact expressed my ideia in a wrong way. So i`ll try to express the ideia in a basic way (so i dont say anything wrong and disrupt it). If you guys could be a little patient with me that would help.

So, I would need to capture the sound coming from a motor. That motor would be, in a first attempt, not moving; just turned on.
I need acess of the spectrogram (frequency x time) in a format that i could use in a statistical software.

My main concerns are: what type of microphone i should use for this application and which setup i need to have acess to that data in a way i can export it to the statistical software.

Thank you guys.
 
So, as a former statistician, software guy (math/numerical analysis was my focus in grad school), and recording dabbler for some time now, I'm going to try to be patient, but you must understand that what you're doing doesn't make a ton of sense from almost any technical viewpoint, at least as simplistically as you describe it.

In any case, this is not a "home recording" kind of thing you're asking about, so you might pose your question on a scientific research forum somewhere, just to get some other opinions while we're trying to imagine what's really going on.

As [MENTION=89697]ecc83[/MENTION] (Dave) says, quantizing sound is done with calibrated tools. You can do this anywhere, anytime, but if you're going to do something scientific, you need a controlled environment, so you need to worry about every bit of sound that's being captured, and that means a contained space for your engine to be running in, with good sound isolation from external noises. And a good exhaust fan, unless this is an electrical motor and not internal combustion?

Now, whether you need a calibrated microphone I think is a good question. If you're trying to establish a baseline, then it's important to know whether it's going to include ultrasonic and subsonic measurement data, because those kinds of microphones are not something most home recorders are interested in, and few of us even have calibrated measurement microphones or sound level meters, which you'd need to correlate the physical volume level (dB) at the microphone against the waveform captured digitally. (I'm leaping at the conclusion you'll want this data in a computer - something you've not explicitly stated.)

Once the sound(wave) is captured in the PC, you can do spectrum analysis on that. If the microphone is not flat (and practically none are), you'd have to bias it against the microphone's response that you recorded with a flat input (white noise or sweep). Keep in mind the room where the motor is located will add a great deal and "unflatten" anything recorded unless it's is essentially an anechoic chamber.

If all you want to do is compare scenario A vs B, eg., the motor at idle vs at 2x idle RPM, then you may not need to calibrate the microphone, but you still need the room to not be contributing additional data to the recording, which it will do if it doesn't absorb all frequencies equally.

Any test case at t0 vs t1 would need to use the same microphone, always tested to insure it still recorded sounds the same way, whether you were validating its flatness or simply that it produced the same output for the same input.

I still think if you are just measuring volume at different frequencies under different load conditions (e.g.), any good microphone can provide enough information to provide good data. The space where you are measuring will be the problem.

P.S. A USB microphone or a microphone via a USB audio interface will put data into a computer. Audio software can generate a statistical analysis of a section of the recorded wave form. You can do what you want with that.

P.P.S. Earthworks is the company I'm familiar with that produces good measurement microphones:
Measurement Microphones — Earthworks Audio
 
I think what you need is the earthworks type mic - including the Behringer version which is a similar design - omni direction. This is critical because cardioid microphones change their spectral response as the sound source gets closer. The bass increases - so for measurement and analysis purposes the distance and angle the mic is at has to be repeated. There is somebody who markets an engine assessment tool that incorporates a measurement mic that the engineers use to hear the sound from each area of the engine to localise where faults are. Flat response, omnidirectional polar pattern. The people who use sound analysis software use these mics too, to get a representation of sound in a space, so they can analyse it and reduce issues with the sound.
 
keith.rogers said:
Audio software can generate a statistical analysis of a section of the recorded wave form.
Click to expand...
There is software that will take a waveform and spit out a detail table of loudness (dB) and frequency content per sample point/time?

One thing the OP mentioned was 'frequency' - I hope he realizes that the sound from an engine will not be ONE frequency but very much a combined bunch of sounds from different parts of the engine - multiple frequencies. And where the mic is placed in relation to the engine will have a significant impact on what is recorded. And if he wants to do this with an engine outside a vehicle (on a 'stand' in a garage) and wants to simulate load, acceleration and other factors, he'll need a dynamometer.
 
mjbphotos said:
There is software that will take a waveform and spit out a detail table of loudness (dB) and frequency content per sample point/time?
...
Click to expand...
Well, sure, it can look at a sample and detail the frequencies contained and relative amplitudes of those frequencies. Audacity can do that with some minimum sample size. Correlating the waveform dB to room dB is something that would have to be done when they calibrate the microphone in the room, using the measurement mic and a [calibrated] sound level meter.

I could be misunderstanding what you're asking, or [still] exactly what OP intends to do, or how they will make this data valid enough to be useful.
mjbphotos said:
One thing the OP mentioned was 'frequency' - I hope he realizes that the sound from an engine will not be ONE frequency but very much a combined bunch of sounds from different parts of the engine - multiple frequencies. And where the mic is placed in relation to the engine will have a significant impact on what is recorded. And if he wants to do this with an engine outside a vehicle (on a 'stand' in a garage) and wants to simulate load, acceleration and other factors, he'll need a dynamometer.
...
Click to expand...
And yes, the sounds from a motor come from all over, so a single mic was a problem for me in the initial set of back and forth. If it's something like an automobile engine, the fan(s), pumps, pulleys and external mechanical parts at the front would largely mask any internal sounds. But, without understanding the actual reason for what's being done, this is turning into another guessing game. Maybe it's all about the fan noise!
 
This, RightMark Audio Analyzer. Products. Audio Rightmark will give a snapshot frequency by dB level graph. It only works with 16 bit 44.1kHz .wavs AFAIK but it is easy and free.

I am glad far better brains than mine have picked up the baton but I shall keep a watch. A change from a "produceha" wanting to do beats with a 2 bob mic and a phone!

Dave.
 
ecc83 said:
This, RightMark Audio Analyzer. Products. Audio Rightmark will give a snapshot frequency by dB level graph. It only works with 16 bit 44.1kHz .wavs AFAIK but it is easy and free.

I am glad far better brains than mine have picked up the baton but I shall keep a watch. A change from a "produceha" wanting to do beats with a 2 bob mic and a phone!

Dave.
Click to expand...

I think the OP wants a time-line graph that would show combined dB at each time point, then the secondary part would be the frequency content - but of course as we have discussed he's thinking "one frequency", not the combined sound that will be the result. I'm sure that those numbers form this software would need to be transferred into a spreadsheet manually for each analysis point, it would not be a "run the engine for a while and read the results in the spreadsheet" thing without a fair amount of work.
 
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