Using the auto levels for XL1s mic audio at DVinfo.net

Josh Bass · August 8th, 2002, 03:55 AM

When setting the mic levels on the XL1s, is it recommended to use the auto setting? I've always done manual because I remember reading somewhere that auto was not recommended. Some other opinions would be nice.

It seems the auto level would keep the sound from peaking.

Don Palomaki · August 8th, 2002, 06:21 AM

Auto audio gain mode generaly gives reasonable results. And it saves trying to ride audio levels if shooting in a changing environment, The reuslts are far better than AGC mode on most moderate priced camcorders. However, best to try it in your applications and see if you are satisfied with the results.

Josh Bass · August 8th, 2002, 11:30 AM

But how does it know how to regulate the sound before someone even begins speaking? That's what concerns me. I don't want the first few words someone says to be too high or low, and then level off.

Don Palomaki · August 8th, 2002, 03:26 PM

That is the trick of AGC. It looks at the leading edge of the audio waveform and if it looks like it is going to be loud (risign very fast) it reduces the gain very quickly (in a matter of a few milliseconds), and then it is farily slow to increase it again. That works for most natural sound sources. But you may have siturations where it does not work (e.g., gun shots)

Ralph Keyser · August 8th, 2002, 03:35 PM

The short answer, Josh, is that it doesn't. It's like automatic exposure in that it adjusts on the fly based on the current input.
It can do OK for many sound sources, but be aware of what you are getting. When the sound is soft, if will pump up the gain. When the sound is loud, it will cut the gain down. The bad part is that the AGC (automatic gain control) is always a beat behind.

With digital audio, however, things get really ugly when the signal clips. You run out of bits to represent the sound, and it's just like overexposing the highlights in the video signal. Therefore, you never want to exceed that 0db point on the audio meters. The best bet is to have a dedicated sound guy and manual level settings. It's really hard to pay attention to sound and picture at the same time. If you're stuck, using the AGC may help you out, but it's a lot like using the automatic exposure control on the camera.

James Emory · August 8th, 2002, 03:53 PM

I agree NOT to rely on auto if you can help it. It's bitten me a few times with clipping. I would only use it for a lock down camera situation where you couldn't ride the meters or get an accurate manual setting before hand. Levels in the EVF (switchable that is) would really be nice instead of some of that other crap!

Josh Bass · August 8th, 2002, 04:00 PM

You said O db is what it's not supposed to exceed?
I swear on my camera that the magic point looks to be 12. . .that's the number that highlighted, anyway.

Rik Sanchez · August 8th, 2002, 05:56 PM

I've been setting my audio so it just barely goes over 12 and it's been a little low, some friend's gave me some audio to put in and they had their set to 0. My audio next to theirs sounded very low.

So as long as the peaks don't go over 0 then I should be okay, right? With the peaks going around the 6 to 2 region, is that the sweet spot? If it isn't, then what would be the audio sweet spot?

Don Palomaki · August 9th, 2002, 06:43 AM

If your XL1 audio meter is peaking in the -6 to -2 range, you should be OK.

If other people give you material that is recorded with average levels much higher, they may have used purely consumer camcorders with traditional consumer AGC, which in general is VERY BAD. The auto gain on the XL1 and GL1 is better than traditional consumer camcorder AGC being in many respects more like a limiter, but it still is a form of AGC and if driven with high signal levels will overcompress the sound as well. As noted above, a good sound (wo)man can do better under most circumstances.

For best sound using the XL1 as the sound recorder, I suggest using quality mics with high output, use the MIC ATT setting to get the best noise floor from the XL1 preamps, use 16-bit/48 kHz record mode, use manual gain and keep the sound peaks below 0 dB on the XL1 meter, and do any level adjustments, compression, etc, in post using quality sound editing gear.

Vic Owen · August 11th, 2002, 11:43 AM

Don's comments are right on. Once you have the audio captured, you can set it in post to any level you want. Most consumer cameras record way too hot. Avoid peaking near 0 on the meter-- any excursions over 0 equal severe distortion.

Jon Eriksson · August 14th, 2002, 08:06 AM

<<<-- Originally posted by Josh Bass : You said O db is what it's not supposed to exceed?
I swear on my camera that the magic point looks to be 12. . .that's the number that highlighted, anyway. -->>>

If you put bars and 1kHz signal, it should be on -12, but when recording it is fine to exceed -12 but as has been stated before NEVER put yourself at risk of clipping by going over 0, so a safe peak would be at -6/-4... I would also suggest that you do manual audio if possible to avoid the nasty pumping of the levels that can occur.

Hope this helps

Regards
Jon

Josh Bass · August 14th, 2002, 11:20 AM

Yeah, yeah, you're right. Zero looks to be the absolute highest you can go.

August 8th, 2002, 03:55 AM	#1
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	Using the auto levels for XL1s mic audio When setting the mic levels on the XL1s, is it recommended to use the auto setting? I've always done manual because I remember reading somewhere that auto was not recommended. Some other opinions would be nice. It seems the auto level would keep the sound from peaking. __________________ The Bass' camerawork The Bass on IMDB

August 8th, 2002, 11:30 AM	#3
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	But how does it know how to regulate the sound before someone even begins speaking? That's what concerns me. I don't want the first few words someone says to be too high or low, and then level off. __________________ The Bass' camerawork The Bass on IMDB

August 8th, 2002, 03:53 PM	#6
James Emory Regular Crew Join Date: Aug 2002 Location: Atlanta, Georgia Posts: 1,892	Auto Gain I agree NOT to rely on auto if you can help it. It's bitten me a few times with clipping. I would only use it for a lock down camera situation where you couldn't ride the meters or get an accurate manual setting before hand. Levels in the EVF (switchable that is) would really be nice instead of some of that other crap!

August 8th, 2002, 04:00 PM	#7
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	You said O db is what it's not supposed to exceed? I swear on my camera that the magic point looks to be 12. . .that's the number that highlighted, anyway. __________________ The Bass' camerawork The Bass on IMDB

August 8th, 2002, 05:56 PM	#8
Rik Sanchez ChorizoSmells Join Date: Apr 2002 Location: Osaka, Japan Posts: 424	I've been setting my audio so it just barely goes over 12 and it's been a little low, some friend's gave me some audio to put in and they had their set to 0. My audio next to theirs sounded very low. So as long as the peaks don't go over 0 then I should be okay, right? With the peaks going around the 6 to 2 region, is that the sweet spot? If it isn't, then what would be the audio sweet spot? __________________ ChorizoSmells Video Barrio Tamatsukuri, Osaka, JAPAN

August 8th, 2002, 06:21 AM	#2
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	Auto audio gain mode generaly gives reasonable results. And it saves trying to ride audio levels if shooting in a changing environment, The reuslts are far better than AGC mode on most moderate priced camcorders. However, best to try it in your applications and see if you are satisfied with the results.

August 8th, 2002, 03:26 PM	#4
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	That is the trick of AGC. It looks at the leading edge of the audio waveform and if it looks like it is going to be loud (risign very fast) it reduces the gain very quickly (in a matter of a few milliseconds), and then it is farily slow to increase it again. That works for most natural sound sources. But you may have siturations where it does not work (e.g., gun shots)

August 8th, 2002, 03:35 PM	#5
Ralph Keyser Major Player Join Date: Aug 2002 Location: Albuquerque, New Mexico USA Posts: 287	The short answer, Josh, is that it doesn't. It's like automatic exposure in that it adjusts on the fly based on the current input. It can do OK for many sound sources, but be aware of what you are getting. When the sound is soft, if will pump up the gain. When the sound is loud, it will cut the gain down. The bad part is that the AGC (automatic gain control) is always a beat behind. With digital audio, however, things get really ugly when the signal clips. You run out of bits to represent the sound, and it's just like overexposing the highlights in the video signal. Therefore, you never want to exceed that 0db point on the audio meters. The best bet is to have a dedicated sound guy and manual level settings. It's really hard to pay attention to sound and picture at the same time. If you're stuck, using the AGC may help you out, but it's a lot like using the automatic exposure control on the camera.

August 9th, 2002, 06:43 AM	#9
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	If your XL1 audio meter is peaking in the -6 to -2 range, you should be OK. If other people give you material that is recorded with average levels much higher, they may have used purely consumer camcorders with traditional consumer AGC, which in general is VERY BAD. The auto gain on the XL1 and GL1 is better than traditional consumer camcorder AGC being in many respects more like a limiter, but it still is a form of AGC and if driven with high signal levels will overcompress the sound as well. As noted above, a good sound (wo)man can do better under most circumstances. For best sound using the XL1 as the sound recorder, I suggest using quality mics with high output, use the MIC ATT setting to get the best noise floor from the XL1 preamps, use 16-bit/48 kHz record mode, use manual gain and keep the sound peaks below 0 dB on the XL1 meter, and do any level adjustments, compression, etc, in post using quality sound editing gear.

August 11th, 2002, 11:43 AM	#10
Vic Owen Major Player Join Date: Dec 2001 Location: Seattle, WA Posts: 540	Don's comments are right on. Once you have the audio captured, you can set it in post to any level you want. Most consumer cameras record way too hot. Avoid peaking near 0 on the meter-- any excursions over 0 equal severe distortion. __________________ -- Vic Owen --

August 14th, 2002, 08:06 AM	#11
Jon Eriksson Regular Crew Join Date: Aug 2002 Location: London, UK Posts: 42	<<<-- Originally posted by Josh Bass : You said O db is what it's not supposed to exceed? I swear on my camera that the magic point looks to be 12. . .that's the number that highlighted, anyway. -->>> If you put bars and 1kHz signal, it should be on -12, but when recording it is fine to exceed -12 but as has been stated before NEVER put yourself at risk of clipping by going over 0, so a safe peak would be at -6/-4... I would also suggest that you do manual audio if possible to avoid the nasty pumping of the levels that can occur. Hope this helps Regards Jon __________________ Real Men do not Preview

August 14th, 2002, 11:20 AM	#12
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	Yeah, yeah, you're right. Zero looks to be the absolute highest you can go. __________________ The Bass' camerawork The Bass on IMDB