RedShark News

25 Apr

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

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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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  • I think you are on about the $35 TomTop shotgun mic? It is a HTDZ HT-81 and it works great and does not sound like " talking to you down a vacuum cleaner tube" at all.

    I know you said "probably" so I can' fault you on that. But if you are looking for a good sounding shotgun and you are on a budget then this is the one for you.

    The link to this mic is http://bit.ly/tomtopshotgunmic

    1 Like
  • That's good news Jack. For a long and probably lightweight shotgun microphone, it is exceptional value for money.

    0 Like
  • I'm getting decent results with a £25.00 iRig Pre between camera and XLR mic. The Pre is fitted with a 4-pole 3.5mm jack intended for iPads and the like, but you can use a 2x2-pole adapter to split the mic input and headphones. An alternative is to do a relatively simple hack (search through Google for iRig Pre hack) which lets you plug straight into cameras and audio recorders. Not a serious solution by any means, but worthwhile.

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  • Yes, thanks for that helpful information. The modified or 'hacked' 'iRig Pre' seems to be a great low priced phantom powering solution, especially as it uses a single, convenient 9 volt battery. However, my concern is that if any high quality microphone is used in conjunction with the iRig, it will pass through two pre-amps: the one in the iRig and the one in the video camera. Alternatively, plugging a Rode NTG3 directly into the Tascam DR-40 will probably 'sound' better in the final mix as the DR-40's 24/96 PCM file is the first generation recording. (an audio link can also be sent from the DR-40 to the video camera's aux input as a backup or 'sync' copy)

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  • You could also use professional small devices, that provide phantom power via one 9Volt battery, like the MZA 14 P 48 U from sennheiser. Or take the two channel sounddevices mixer. But when you talk about professional tools, then please talk about them and not about strange things.

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  • I think it is worth to point out a 3rd way of recording in DSLRs. There are external recorders (Zoom, Tascam, ...) sound mixers (Beachtek, Juicedlink ...) and just simple or complex cables... Simple cable: unbalanced ones. Complex cables: balanced to unbalanced with HQ signal transformer inside. That, for me, it's been the best solution to THE audio problem in DSRLs world. I did some tests and now I'm using it in everyday work:
    http://pospotime.wordpress.com/2013/03/12/improving-dslr-audio-the-3rd-way/

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  • Yes, correct cables are important and the best way of converting a balanced mic to an unbalanced DSLR microphone input is by using a line impedence matching transformer. These ($15) items convert the 3 wire XLR cable to 2 wire mic cable and match impedence at the same time but my search in the original article was for a cost effective way to do this AND generate 48 volt phantom power as well. To my mind, the Tascam DR-40 @ around $140, still offers the 'most for the least'.

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  • Yes, but as always cost effectivness and buying the cheapest product are different things. I would not trust a thing like that to have a proper Analog/Digital-conversion. I would also never buy the mentioned rode-boom, its much much to heavy and it is easyer to break/deform, than for example the carbon ones from ambient.

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  • I agree the Rode boom is heavier than a carbon fibre one but it came bundled with my NTG3 ENG package which I bought new, used once indoors, for less than half the normal price so I'll live with that. I think you'll find many will agree that the pre-amps and A/D converters in the Tascam DR-40 are of adequate if not excellent quality. Remember, the bottom line here is I'm attempting to get the best sound and picture possible from an 8 bit pro-sumer video camera and this audio configuration combined with my use of vintage Carl Zeiss prime lenses, currently offers me an excellent and cost effective solution for my current market.

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