Wednesday, 19 March 2014

In search of better screencasting audio

I have been using my surface pro for screen casting every now and then and am slightly frustrated with a few things.  I'm after clear video, great audio and a small file size.  Not much to ask :-)

On one course I use bb flashback to record live lectures (as opposed to our usual automated lecture recording system provided by the university).  The audio gives me speech that is perfectly understandable but there is quite a bit of background noise and it isn't that pleasant to listen to.  I noticed that even when recording in my office I still get a fair bit of background noise when using the built-in microphone.   I suspect it is picking up my office air conditioning and it is definitely picking up the surface fan when it kicks in.  This is a problem I want to solve.  Initially I thought it would be as simple as shelling out $20-$50 for a decent external microphone.  Turns out it isn't that simple.

I've been doing some reading around audio recording and after trialling a bunch of different microphones and audio interfaces have come to the following conclusions:

a) to avoid electronic noise, use usb
b) to avoid background noise from the environment use a good quality directional dynamic microphone (as opposed to a condenser)
c) microphones may need an amplifier to boost the signal
d) if you want really nice audio, expect to shell out a lot for it (e.g. around $500 NZ)

I'll deal with each conclusion in turn.

Cheap external computer microphones (or headset microphones) will often plug into the 3.5mm jack on a laptop.  With the surface pro I have found that every microphone that I've plugged into a 3.5mm jack has had issues with noise.  My brother who is an electrical engineer (and audiophile) told me that using the 3.5mm jack and onboard circuits for sound processing is likely to result in noise.  The included soundcard on portable computers isn't going to be ideal for processing high quality audio.  It is better to ditch the 3.5mm jack and get your audio in via the usb connection (so that the signal processing can be done externally).  There are a number of well known microphone manufacturers who produce microphones that plug directly into a usb port.  Here are a list of the ones I considered after extensive research: the Rode podcaster, the Blue Snowball, the Blue yeti, the Studio projects LSM, the Samson Go-mic and the Audio-Technica ATR2100 USB.  You can find youtube reviews on all of these but the most useful site I found was Recording Hacks: http://recordinghacks.com/
All these microphones come highly recommending for podcasting.

Microphones fall into two main categories, condenser microphones (which use a capacitor) and dynamic microphones (which use a magnet and coil).  Condenser microphones tend to be much more sensitive and also need to be powered.  I tried out a few condenser mircophones (e.g. the Blue Snowball and Blue Yeti) and while the audio was very clear and electronic noise wasn't an issue, background noise was.  Despite these microphones having cardiod pickup patterns (which means in theory they only pick up noise in front of them, rather than from all around) condensers are so sensitive that I as picking up noises from behind the microphone at the very far end of the shop I was in.  Condensers would be great in a studio environment with sound proofing where background noise wasn't an issue.  Since I have air conditioning on in my office, plus a computer fan and the sound of me writing on my surface with a stylus, condensers weren't going to work.  By contrast the dynamic cardiod microphones I tried were MUCH better at picking up just my voice and no background noise.  They are less sensitive so you have to position your mouth a lot closer to the microphone but this is a small price to pay for less noise.  The Rode podcaster did a lot better job of isolating my voice, even though I was testing it in a relatively noisy shop.

Unfortunately the Rode podcaster didn't give me very high input levels so I had to post process the audio recordings and massively scale the gain.  It appears that this is a common complaint with usb microphones and that it is often necessarily to increase the amplitude of the signal.  While you can do this in software, increasing the signal via post processing can also introduce audible background noise (that wasn't noticeable until you increase the amplitude).  A better solution is to use a pre-amp (pre-amplifier) to increase the signal.

If you are going the route of using a pre-amp, then you need an audio-interface, which does the job of both amplifying the microphone's signal and converting the signal to a digital format so that it can go in via usb.  The nice thing about going with this route is you are no longer limited to usb microphones, you can use professional audio microphones which make use of the standard XLR connectors present on just about all mics used in the recording industry.  I tried out The Shure SM57 instrument mic (an industry standard) with my brother's audio interface (a TASCAM audio interface ) and got fantastic quality.  This may well be the way to go.

In summary, to get really good audio you will probably need a good audio interface (for around $200-$300) plus a good dynamic microphone (for around $150-$250) plus stand and cable.
I've been looking at the Shure SM58 or SM48 for the microphone and the Onyx Mackie blackjack as the interface.

My last hope at a cheaper solution is the Audio-technica AT2100USB microphone, which is currently out of stock, so I haven't been able to try it yet.









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