Magic Lantern Forum

Using Magic Lantern => General Help Q&A => Topic started by: eibr on September 29, 2013, 12:37:26 PM

Title: Boosting analog gain or +20dB on Videomic Pro?
Post by: eibr on September 29, 2013, 12:37:26 PM
Hello forum.

This is my first post here, since I downloaded an installed Magic Lantern on my Eos 5d mark II yesterday. I love the features in audio control and focus/exposure assist. I need to dig deeper both on the camera and on this forum.

I have a question that cant wait for me to dig into the forum :)
I have a Røde Videomic Pro to go with my EOS 5D mark II camera. The Videomic Pro has a +20dB option which is a useful feature. I have used it a lot in interview situations where I only have on-camera microphone. If I need more audio, should I use this +20dB option before boosting the analog gain setting within Magic Lantern? I have of course set AGC to "off".

Best regards,
Eirik Berger
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: N/A on September 29, 2013, 07:46:00 PM
Do a test, record the same sound source with the Rode set to +20, and then another one with the camera set to +20, then listen to them. You could even upload the wav's and post a link,  I'm kinda interested to hear the results.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: 1% on September 30, 2013, 02:30:29 AM
Depends on if you trust the canon amplifier or the one on the mic.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: ItsMeLenny on September 30, 2013, 05:22:14 AM
I have the Stereo Video Mic (not pro), it doesnt have the +20, but I boost the analogue in the camera right up, however I do not touch the digital, it is absolutely terrible. Turn on the +20 first and if you still need more volume boost the analogue in ML, if you still need more volume do not touch the digital, instead boost it in post.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: 1% on September 30, 2013, 05:38:12 AM
Through the headphones it souds like the digital really boosts the noise floor. You can hear all the background.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: Audionut on September 30, 2013, 05:42:16 AM
It's just like ISO.

Analog does a great job of boosting the signal while retaining a low noise floor and hence, dynamic range.
Digital is simply boosting the already captured signal.  It's boosting the entire signal by the specified amount, including the noise floor.

As Lenny mentions, if you need digital boost you should do it in post so that you have a chance of recovering the noise floor.

Try a 2 pass noise reduction.
Slight noise reduction on the input, digital gain, and then further noise reduction as needed.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: eibr on September 30, 2013, 09:54:28 PM
I did a brief test with myself 44 inches in front of the camera/mic, which will be about the distance for my field interviews this week.
I tried all Analog Gain settings from 20 to 32 dB with and without the +20dB setting on the Røde Videomic Pro. The most pleasing sound (speech) were with analog gain within ML set to 23 dB and with +20dB on the mic.

I do not touch digital gain.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: pilgrim on October 01, 2013, 12:54:54 AM
I don't know if your mic is stereo. In case stereo, try also to put gain +6dB in one channel, if this channel clipping you still have other channel not clipping. Normally +6dB digital gain still acceptable. If the micro is mono, use also the internal microphone to record. Maybe you can use as a background on post production (even with the stereo effect softly), or maybe to get the noise print for the noise reduction, or backup if the main micro is clipping. One more note, find a really good cable especially if not XLR. In the long term it's important. Very often the quality of cable is under estimate.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: N/A on October 01, 2013, 06:04:25 AM
Aim for a peak of -9db or lower, the closer you get to 0db the more you'll clip your converter. This actually goes for most any a/d audio converters. With crappy converters like on our cameras your ideal range is between -10 to -20db, but some of the nice converters like Apogee, Prism, etc. would allow you to record -40 and below, since the noise floor is somewhere around -96db if memory serves correctly.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: Audionut on October 01, 2013, 06:21:27 AM
16bit will give you dynamic range of 96dB (http://en.wikipedia.org/wiki/Audio_bit_depth#Quantization).

You could join in the loudness war (http://en.wikipedia.org/wiki/Loudness_war) and clip to your hearts content.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: Africashot on October 01, 2013, 06:40:38 AM
I don't know if your mic is stereo. In case stereo, try also to put gain +6dB in one channel, if this channel clipping you still have other channel not clipping. Normally +6dB digital gain still acceptable. If the micro is mono, use also the internal microphone to record. Maybe you can use as a background on post production (even with the stereo effect softly), or maybe to get the noise print for the noise reduction, or backup if the main micro is clipping. One more note, find a really good cable especially if not XLR. In the long term it's important. Very often the quality of cable is under estimate.

This is really interesting advice but I am now sure you have never used or even seen a Rhode Video Mic pro!
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: N/A on October 01, 2013, 08:26:41 AM
16bit will give you dynamic range of 96dB (http://en.wikipedia.org/wiki/Audio_bit_depth#Quantization).

You could join in the loudness war (http://en.wikipedia.org/wiki/Loudness_war) and clip to your hearts content.
Sonnox Inflator  ;D
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: Audionut on October 03, 2013, 08:22:39 AM
Sonnox Inflator  ;D

Just gain it and let kids hear the clipping they want :P  Clipping is loud, clipping is good.  BOOM  BOOM BOOM  DOOF DOOF DOOF.  Listen to my boot lid vibrating bro, DAT BASS!

Such a shame they are mixing movies hot too.  I want to be frightened when that 115dB peak hits.  Not have to settle for a 100dB peak because I need to have the volume -15dB below reference so I don't damage my ears further from the constant LOUD!
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: ItsMeLenny on October 03, 2013, 01:20:39 PM
Listen to my boot lid vibrating bro, DAT BASS!

I read that as "boot lid vibrato".

Boot rattle will hopefully cause as much damage to their cars as what's already been done to their heads.

DVD-video had audio standards. CD's didn't, I don't think tape did either, cassette tape clipping is terrible, it turns into triangle waves, sawtooth.

Vinyl has standards, but people just compress the audio to the extent where the waveform matches the clipped CD.
Title: Re: Boosting analog gain or +20dB on Videomic Pro?
Post by: Audionut on October 04, 2013, 06:19:59 AM
CDs were invented back in a time when the destructive nature of digital clipping outweighed the perceived loudness benefits.

DVD/blu-ray (more importantly the audio formats contained within) have standards, yes.  But that doesn't stop the sound engineer mixing it however he/she wants.  The standards (with regards to mixing levels etc) are merely recommendations.  They are not defined, as in, it must be 16bits or it will not play, for example.

A blu-ray with the centre channel mixed 10dB to hot will play just fine.