Exploring Sound Design Tools: Hydrophone

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This post belongs to a series where I´m using unconventional microphones to get interesting sounds.
Please have a look at the other posts from the series:

Contact Microphone.
Coil Pickup.

Continuing with the unconventional microphones theme, this time I've being fooling around with an hydrophone. As you may know, these are designed to better capture sound in water instead of in the air.

I tried recording water movements and props on all sorts of small containers, the kitchen sink and the bathtub. I quickly learned that is important to manage the cable properly since moving or touching it can be quite noisy, specially when trying to get quiet sounds. I was usually using one hand to keep the microphone and cable still and the other to perform the sound.

I also discovered that very small changes in mic placement usually produce vastly different results. On some occasions, just some centimetres were the difference between a close aggressive sound and a distant atmospheric one. I don't know if this is the case because water is denser than air and sound waves move 4.3 faster but it certainly something to keep in mind.

Finally, I have to say I was surprised by how clean the sounds were, although when processing very quiet stuff I did some RX cleaning here and there.

So, on with the recordings. You can individually download every sound via freesound.org or download the whole package through this link.

Bubbles

I first tried to get some bubble sounds. I used a plastic drinking straw to get the small ones and then tried sinking a bowl or a mug with some air inside to get bigger ones.

I tried some effervescent tablets too and got some nice fizzy sounds. 

Movements

Next, I tried some water movements. I quickly found out that submerging the microphone and trying to create water sounds with hand movements doesn't work really well since not a lot of sound energy reaches the mic.

So I tried to record them with the mic just on the surface of the water and got better results that you can hear in the first example below.

I also wanted to get some underwater movements and discovered that the easiest way was to move the microphone itself through a large mass of turbulent water. I did this in a filled bathtub (second recording below).

Steady Water Streams

For this sounds, I was trying to get long samples of water flowing that could be then used for underwater scenes.

To achieve this, you need some kind of water flow. In my case, since I didn't have access to a swimming pool or a jacuzzi, I just recorded the whole filling and emptying process of a kitchen sink and a bathtub.

While doing this, I experimented with different mic placements and amounts of water flowing in. You can get a vast array of result by just changing these two factors as you can hear in these examples:

Metal Kitchen Sink

Here are some other sounds I got in the kitchen sink.

Again, the draining sounds show how important mic placement is. Those changes in the sound intensity were produced by just getting closer or further away from the vortex.

Others

Here are some other random things I tried.

The first one is just me hitting a floating bowl with my finger. The resonance was captured with the mic underwater and close the bowl but not touching it. As the bowl filled more and more, the pitch changed in an interesting manner.

Lastly, the second recording below is how water directly impacting the hydrophone sounds. 

Conclusions

It was nice doing this recording session. I learned that mic placement is crucial when working with these microphones. Having an hydrophone is perhaps kind of a niche purchase, but it could be very useful if you need underwater sounds or want to record anything that involves too much water for conventional microphone to be safe.

Exploring Sound Design Tools: Contact Microphone

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This post belongs to a series where I´m using unconventional microphones to get interesting sounds.
Please have a look at the other posts from the series:

Hydrophone.
Coil Pickup.

I bought a JrF contact microphone a while ago to do some experimenting and see the potential these mics have for sound design. Here is what I've discovered.

As you may know, a contact microphone records sound from vibrating solid materials instead of the air. This gives these microphones some unique and interesting sonic qualities. Since we are not capturing the ambience around the recording, results usually feel isolated, without an acoustic context. This can be a blessing, no need to worry about reverb or background noise but also may result in dull boring sounds. I quickly discovered than experimenting and trying different props, microphone positions and methods of producing the sound is key to achieve interesting results.

On the technical side, contact microphones need to be connected to a high impedance input in order to have a good frequency response. If you want to get into more detail about this and contact microphone usage in general this is the place to go.

Now that you know the deal, here are some of my recordings. You can individually download every sound via freesound.org or download the whole package through this link.

Window Glass

I just attached the microphone to a large window and try different things.

The first three sounds were recorded with just damp hands, I was trying different movements and was surprised with some of the results, although most of it is just regular squeaks. 

As you can hear, something so simple creates a surprising amount of low end some times.

Next, I tried to try using a milk frother applied on the glass. These recordings exemplify very well the possibilities of these microphones. Usually, it would be impossible to avoid the sound of the machine itself but with a contact mic we are getting the sound of the glass reacting to the vibration without any of the motor. 

The first two examples show this. The other two are the result of applying the forther to the cable of the mic itself resulting in some weird and tonal sounds.

 

Metal Oven Tray

Next, I tried to record some impacts on a metal oven tray. No thing too remarkable on this one but I got nice clean metal resonances that are always good to have.

On the first recording, you will hear that the three small impacts sound kind of distorted. This happens when the microphone is loose so it vibrates against the surface of the object you are recording. This can be useful if you want to get a dirty sound.

Bicycle

I thought the the wheel spokes would be interesting to record and the sound was surprisingly heavy.

Despite having roughly the same length, different spokes produced very different metal overtones. 

I can see these being use with some dissonance in a horror soundscape.

Electric razor

This razor doesn't have different speeds but I discovered that I can use my finger to slow down the motor and create some interesting power on and power off.

There is a nice amount bass, this could be use as layers for sci-fi or fantasy, weird machines.

For the third sample below I tried to create some malfunctioning engine sounds.

Electric Toothbrush

This one is quite dull but could be used as a layer for a servo door or robot. Also, it has a weird chewbacca kind of tone.

Drying Rack

Nice metal impacts with a lot of resonance. Again, surprised with the amount of bass here.

As you can hear, some of the sound have that distorted quality coming from the microphone being a little loose.

The ratchet/castle door sound was done by just striking the different metal rods with a wooden spoon. Quite cool.

Printer

Lastly, I tried attaching the mic to my printer. The result is not very interesting but it could be nice as layers for a robot or some mechanical thing.

Conclusions

As you can see, metallic objects are probably the most interesting ones to record as they resonate more but I'm sure there are many other creative things to try with a contact microphone that I will explore in the future. Thanks for reading.

Shotgun Microphones Usage Indoors

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Note: This is an entry I recovered from the old version of this blog and although is around 5 years old (!), I still think the information can be relevant and interesting. So here is the original post with some grammar and punctuation fixes. Enter 2012 me:

So I have been researching an idea that I have been hearing for a while:

"It’s not a good idea to use a shotgun microphone indoors."

Shotgun microphones

The main goal of these devices is to enhance the on axis signals and attenuate the sound coming form the sides. In other words, make the microphone as directional as possible in order to avoid unwanted noise and ambience.

To achieve this, the system cancels unwanted side audio by delaying it. The operating principle is based on phase cancellation. At first, the system had a series of tubes with different sizes that allowed the on axis signals to arrive early but forces the off-axis signals to arrive delayed. This design, created by the prolific Harry Olson eventually evolved in the modern shotgun microphone design.

Indirect signals arrive delayed. Sketch by http://randycoppinger.com/

In Olson’s original design, in order to improve directivity you had to add more and more tubes, making the microphone too big and heavy to be practical. To solve this, the design evolved into a single tube with several slots that behaved in an equivalent manner to the old additional tubes. These slots made the off-axis sound waves hit the diaphragm later, so when they were combined with the direct sound signal, a noise cancellation occurred, boosting the on-axis signal.

This system has its limitations. The tube needs to be long if we want to cancel low enough frequencies. For example, a typical 30 cm (12″) microphone would start behaving like a cardioid (with a rear lobe) under 1,413 Hz. If we want to go lower, the microphone would need to become too big and heavy. Like this little fellow:

Electro Voice 643, a 2 meters beast that kept it directionality as low as 700 Hz. Call for a free home demostration!

On the other hand, making the microphone longer makes the on-axis angle narrower, so the more directive the microphone is, the more important is a correct axis alignment. The phase cancelation principle also brings consequences like comb filtering and undesirable coloration when we go off axis. This can work against us when is hard to keep the microphone in place, hence this is why these microphones are usually operated by hand or on cranes or boom poles.

In this Sennheiser 416 simplified polar pattern, we can appreciate the directional high frequencies (in red) curling on the sides. The mid frequencies (in blue) show a behaviour somewhere between the highs and a typical cardioid pattern (pictured in green) with a rear lobe.

mg19shotgunrotated.jpeg

This other pattern shows an overall shotgun microphone polar pattern. The side irregularities and the rear lobe are a consequence of the interference system.

Indoor usage

The multiple reflections in a reverberant space, specially the early reflections, will alter how the microphones interprets the signals that reach it. Ideally, the microphone, depending of the incidence angle, will determine if the sound is relevant (wanted signal) or just unwanted noise. When both the signal and noise get reflexed by nearby surfaces they enter the microphone in “unnatural” angles (If we consider natural the direct sound trajectory). The noise then is not properly cancelled since it does not get correctly identified as actual noise. Moreover, part of the useful signal will be cancelled, because it is identified as noise.

For that reason, shotgun microphones will work best outdoors or at least in spaces with good acoustic treatment.

Another aspect to have in mind is the rear lobe that these microphones have. Like we saw earlier this lobe captures specially low frequencies so, again, a bad sounding room that reinforces certain low frequencies is something we want to avoid when using a shotgun microphone. When we have a low ceiling, we are sometimes forced to keep the microphone very close to it so the rear lobe and the proximity effect combines and can make the microphone sound nasty. This is not a problem in a professional movie set where you have high ceilings and good acoustics. In fact, shotgun microphones are a popular choice in these places. 

Lastly, the shotgun size can be problematic to handle in small places, specially when we want precision to keep on axis. 

The alternative

So, for indoors, a better option would be a pencil hipercardioid microphone. They are quite smaller and easier to handle in tight spaces and more forgiving in the axis placement. Moreover, they don’t have an interference tube, so we won't get unwanted colorations from the room reflections.

Is worth noting that these microphones still have a rear lobe that will affect even the mid-high frequencies, but not as pronounced.

So hypercardioid pencil microphones are a great choice for indoors recording. When compared to shotguns, we are basically trading off directionality for a better frequency response and a smaller size.