25 Apr 2013

Broadcast quality audio recording with prosumer camcorders and DSLRs

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Pro Audio recording in the field Pro Audio recording in the field Craig Marshall


Broadcast Quality Audio Field Recording with Prosumer Cameras and DSLRs ("Unlocking the Mysteries of ‘Phantom Power"). RedShark contributor Craig Marshall reports

I am now the proud owner of a broadcast quality shotgun (super cardioid) microphone. Although my Sony NEX VG20 camcorder is equipped with a large four piece spatial microphone which will record high quality AC3 stereo and six channel 5.1 Dolby Surround, I have been searching the usual on-line bazars for a portable audio solution which would be more 'directional' than the camera's on-board equipment.

The on-line market place can be a bit of a minefield where audio products are concerned as microphones from Germany compete with 'clones' from China. On eBay for example, you can purchase a genuine and much coveted Sennheiser '416' shotgun for around $1K or a remarkably similar looking little gem from the cheerful Tom Top Wholesalers for about $25 including free international shipping. A bargain?! Probably Not. It may indeed work but any recorded voice would probably sound like it’s talking to you down a vacuum cleaner tube.

As readers of my recent article for RedSharkNews will know, I'm always on the lookout for a good deal but you can now breathe a sigh of relief as I’m not about to waste my hard earned on low quality microphones. Audio is sometimes regarded as the ‘poor cousin’ to HD video and amateur productions can often be distinguished from their professional counterparts by sound quality alone. An investment in quality audio equipment is as essential for me as it should be for you. Nice sounding microphones demand engineering excellence and this costs money. End Of.

Rode Microphone ENG package

I have a complete Rode Microphone ENG package including telescopic boom pole, carry case with shoulder strap, pistol grip, blimp, ‘dead cat’ wind sock, 25’ XLR cable and of course, the magnificent NTG-3 super cardioid shotgun microphone with its dedicated ‘bomb proof’ transport case.  

Now here’s the rub:  like all studio quality microphones, the Rode NTG-3 is fitted with a balanced XLR plug, whereas my camera has a mini 3.5mm stereo auxiliary microphone socket. This problem is easily overcome by using a cheap, transformer-equipped line converter with some plugs & cables but there is an added dimension here. Professional microphones designed for professional cameras require a ‘phantom’ DC power supply - all 48 volts of it! Most HD video cameras and DSLRs operate with 7 to 12 volt batteries and most if not all, are unable to deliver ‘phantom’ power. Dynamic microphones require no power supply but condenser microphones need a small DC voltage applied to the element and in some cases, a 1.5v or 9 volt battery inside the microphone is sufficient. Many professional microphones on the other hand need 48 volts or thereabouts sent up the cable from the audio recorder’s input socket. This is referred to as ‘phantom’ power because the 48 volt Direct Current is mysteriously ‘superimposed’ onto the microphone’s wires and into the element without interfering with or distorting the audio signal. Spooky!

I should explain here the term ‘balanced’ in relation to professional microphones. Consumer microphones generally have two wires in the cable: hot and ground. Think of the ‘hot’ wire as potentially a great long radio aerial. Even though the ‘ground’ shield screens the ‘hot’ wire from interference, any noise or hum present will simply be amplified by the audio device’s preamps along with the signal. Not so good. In a balanced microphone using TRS or XLR connectors, there are three wires. Think of them as ‘hot’, ‘cold’ and ground. Any noise or hum that sneaks past the shield will be present on both ‘hot’ and ‘cold’ wires simultaneously. The differential pre-amps in a professional audio device are very clever as they will ‘see’ the noise on both wires but amplify only the ‘difference’. That is, your audio signal. Cute!


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Craig Marshall

Retired freelance TV commercial and documentory producer/director/camera/editor

Website: www.HDvideo4K.com

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