Unexplainable audio distortion at DVinfo.net

David Arendt · September 6th, 2009, 08:03 AM

Hi,

I used my Z7 yesterday at a wedding reception with the standard microphone. The settings have been the following:

INPUT1 : MIC +48V (the standard microphone is connected on input1)
INPUT2 : MIC (wireless mic receiver)
REC CH SELECT CH1,CH2

So INPUT1 should be recorded on left and right channel and INPUT2 should be ignored (there was also no signal on INPUT2 as the receiver was off during this time)

CH1 was on auto
CH2 was on manual

In the audio menu everything was at default except audio limiting which was on.

At the moment of the distortion CH2 was manually adjusted to stay 4 bars away from red add maximum level.

On CH2 I have especially on bass sound a very strong distortion. In fact only the distortion and not the audio signal can be heard at this channel somrtimes. On CH1 which was on auto the distortion was audible much less and audio was there during distortion.

Does anyone have any idea what could be the cause of the problem ? Should I send the Z7 in for repair ?

Thanks in advance

Rob Morse · September 6th, 2009, 03:33 PM

I use a Z5 but they should be similar. You have the limiter on but what is the trim set at? I personally have never had success with the AGC on cameras. I always use manual. The settings are slightly different on the Z5 because I have the built in mic but I believe if it's set to Ch1,2 it should be recording input 1 on both channels. At least that was how it worked on other cameras i've owned. Have you used that mic before? Was the audio just hot due to a loud venue or was it actual distortion?

Don Bloom · September 6th, 2009, 03:52 PM

AGC on most Sony cams is a soft limiter but you can still overload the sound. Setting it 4 bars below red means nothing. What was the LEVEL (the db the limiter was set to?

If it was anything over -12 it was probably too hot. Were you monitoring with headphones?
If not you should be.
As for the settings I'm not all that familiar with the Z7 but I have owned and used sonys for a long time and they are typically a bit hot anyway so what I suggest is finding out where -12db is and set you audio to not go over that. Setting 1 channel to AGC and 1 to manual is fine as long as you know where the top of the scale is as far as good audio and generally thats at -12.

Like was stated, it might be the venue was 'hot' more than actual distortion. Weh nyou load it into your NLE are the waveforms visible or is one big solid bar across the audio track?
That'll give you an idea whether its 'hot' or distorted.

David Arendt · September 6th, 2009, 10:22 PM

Hi,

I'm not sure if you can change the level of the limiter. INPUT 1 trim was set to the default 0db but for me this seems more to be a preamplifier setting than a limiter setting or am I wrong here ? I am generally using headphones but this camcorder wasn't operated by myself. The person operating it did not use headphones. If I see the waveform in NLE, on channel 1 (auto) I see audio a bit hot in general. On channel 2 which was add manual, waveforms look quite normal and never go higher than 80% (even during distortion). Distortion seems more like a loud crackling sound replacing the audio on channel 2. On channel 1 it is heard, but the audio is still there during it. I was already thinking about the music being too loud for the mic itself to handle, but what I find completely wired is why the problem is much less on CH1 which was hitting often 100% due to AGC. Shouldn't the problem have been the same or even stronger on this channel ?

Thanks in advance

Don Bloom · September 7th, 2009, 06:03 AM

AGC is really more of a soft limiter and since you had it on channel 1 it limited the audio to 0db which in any case is too much to handle. Channel 2 being set to 80% means nothing - 80% of what? When running manual settings for audio one must listen and watch the levels and be able to "ride the wheels" to adjust on the fly as needed.

After reading your description it sounds like the audio was simply "hot" and the audio settings were wrong or at least not set right and the operator did a big no-no by not wearing headphones to monitor and make adjusts on the fly.

You'll need to do some extra work in post to "fix" the sound-I don't think you'll be able save it to perfection but at you should be able to salvage it "listenable"

David Arendt · September 7th, 2009, 10:43 AM

In order to clarify the 80% I will explain my 80% a bit more (as I am writing software, I look it at more on the digital side than on the analog one which might sometimes be a fault).

16 bit audio normally is stored as signed integer going from −32768 to +32767. By 80% I just wanted to tell that in my case, it was going from -26000 to +26000 so there has been room left from the sampling point of view. Sometimes distortion is introduced due to the loudest point being beyond 32767 and the waveform is simply cut. But as here it wasn't touching the 32767 by margin the distortion seems to have occurred in analog circuits prior to sampling.

Nevertheless I told the operator that I never again want to see him without headphones.

Rob Morse · September 8th, 2009, 06:27 AM

David, if the guy wasn't wearing headphones then there isn't much to talk about. It sounds like the guy you were using was inexperienced and I would attribute it to something he did. It sounds like the mic was overloaded and he never would have known. I did this once myself, years ago and it's the best way to learn. As Don mentioned, you can play with it in post but good luck with that. It would be the same as trying to fix video that had the gain turned up all the way.

By the way, the Z5 has a trim adjustment so I would imagine the Z7 does as well. I also have found Sony's to be a little hot on the audio and since I shoot in places with loud music, I set the trim to -6 db and it's worked out. Recently, I started using a Shure SM57 in a wireless setup (along with my usual AT835). I stick it on a mic stand by the DJ speakers. I can honestly say it has made a huge difference when shooting in that environment. The mic can handle the noise and I can move all over the room and keep consistent audio

Zach Love · September 9th, 2009, 03:20 AM

You said that the distortion was on CH2, right? And the audio wasn't maxed out?

If so, it seems like it is the wireless set & not the camera. The audio could get overloaded at the transmitter & then the audio is wasted long before it hits the camera.

What wireless set were you using?

David Arendt · September 9th, 2009, 04:43 AM

The wireless transmitter was connected but ignored as I had the Rec CH switch to CH1,CH2 so the same signal from the on camera mic was recorded on CH1 and CH2.

This is exactly what I don't quite understand. CH1 which was on AUTO and CH2 which was on manual where receiving the signal from the same microphone. However on the AUTO channel which was sometimes maxed out, there was a lot less distortion than on the MANUAL which has not been maxed out.

Zach Love · September 9th, 2009, 11:26 AM

Quote:

Originally Posted by David Arendt

The wireless transmitter was connected but ignored as I had the Rec CH switch to CH1,CH2 so the same signal from the on camera mic was recorded on CH1 and CH2.

Ok I read that & it didn't click. My brain must have been needing more sleep.

September 6th, 2009, 08:03 AM	#1
David Arendt Regular Crew Join Date: Aug 2008 Location: Bereldange, Luxembourg Posts: 41	Unexplainable audio distortion Hi, I used my Z7 yesterday at a wedding reception with the standard microphone. The settings have been the following: INPUT1 : MIC +48V (the standard microphone is connected on input1) INPUT2 : MIC (wireless mic receiver) REC CH SELECT CH1,CH2 So INPUT1 should be recorded on left and right channel and INPUT2 should be ignored (there was also no signal on INPUT2 as the receiver was off during this time) CH1 was on auto CH2 was on manual In the audio menu everything was at default except audio limiting which was on. At the moment of the distortion CH2 was manually adjusted to stay 4 bars away from red add maximum level. On CH2 I have especially on bass sound a very strong distortion. In fact only the distortion and not the audio signal can be heard at this channel somrtimes. On CH1 which was on auto the distortion was audible much less and audio was there during distortion. Does anyone have any idea what could be the cause of the problem ? Should I send the Z7 in for repair ? Thanks in advance

September 6th, 2009, 03:52 PM	#3
Don Bloom Inner Circle Join Date: Jan 2003 Location: Chicago, IL Posts: 6,609	AGC on most Sony cams is a soft limiter but you can still overload the sound. Setting it 4 bars below red means nothing. What was the LEVEL (the db the limiter was set to? If it was anything over -12 it was probably too hot. Were you monitoring with headphones? If not you should be. As for the settings I'm not all that familiar with the Z7 but I have owned and used sonys for a long time and they are typically a bit hot anyway so what I suggest is finding out where -12db is and set you audio to not go over that. Setting 1 channel to AGC and 1 to manual is fine as long as you know where the top of the scale is as far as good audio and generally thats at -12. Like was stated, it might be the venue was 'hot' more than actual distortion. Weh nyou load it into your NLE are the waveforms visible or is one big solid bar across the audio track? That'll give you an idea whether its 'hot' or distorted. __________________ What do I know? I'm just a video-O-grafer. Don

September 7th, 2009, 06:03 AM	#5
Don Bloom Inner Circle Join Date: Jan 2003 Location: Chicago, IL Posts: 6,609	AGC is really more of a soft limiter and since you had it on channel 1 it limited the audio to 0db which in any case is too much to handle. Channel 2 being set to 80% means nothing - 80% of what? When running manual settings for audio one must listen and watch the levels and be able to "ride the wheels" to adjust on the fly as needed. After reading your description it sounds like the audio was simply "hot" and the audio settings were wrong or at least not set right and the operator did a big no-no by not wearing headphones to monitor and make adjusts on the fly. You'll need to do some extra work in post to "fix" the sound-I don't think you'll be able save it to perfection but at you should be able to salvage it "listenable" __________________ What do I know? I'm just a video-O-grafer. Don

September 9th, 2009, 03:20 AM	#8
Zach Love Major Player Join Date: Jul 2006 Location: Chicago, IL Posts: 944	You said that the distortion was on CH2, right? And the audio wasn't maxed out? If so, it seems like it is the wireless set & not the camera. The audio could get overloaded at the transmitter & then the audio is wasted long before it hits the camera. What wireless set were you using? __________________ Nothing says you're a serious video maker like S-VHS

September 6th, 2009, 03:33 PM	#2
Rob Morse Major Player Join Date: Feb 2009 Location: Charlotte, NC Posts: 427	I use a Z5 but they should be similar. You have the limiter on but what is the trim set at? I personally have never had success with the AGC on cameras. I always use manual. The settings are slightly different on the Z5 because I have the built in mic but I believe if it's set to Ch1,2 it should be recording input 1 on both channels. At least that was how it worked on other cameras i've owned. Have you used that mic before? Was the audio just hot due to a loud venue or was it actual distortion?

September 6th, 2009, 10:22 PM	#4
David Arendt Regular Crew Join Date: Aug 2008 Location: Bereldange, Luxembourg Posts: 41	Hi, I'm not sure if you can change the level of the limiter. INPUT 1 trim was set to the default 0db but for me this seems more to be a preamplifier setting than a limiter setting or am I wrong here ? I am generally using headphones but this camcorder wasn't operated by myself. The person operating it did not use headphones. If I see the waveform in NLE, on channel 1 (auto) I see audio a bit hot in general. On channel 2 which was add manual, waveforms look quite normal and never go higher than 80% (even during distortion). Distortion seems more like a loud crackling sound replacing the audio on channel 2. On channel 1 it is heard, but the audio is still there during it. I was already thinking about the music being too loud for the mic itself to handle, but what I find completely wired is why the problem is much less on CH1 which was hitting often 100% due to AGC. Shouldn't the problem have been the same or even stronger on this channel ? Thanks in advance

September 7th, 2009, 10:43 AM	#6
David Arendt Regular Crew Join Date: Aug 2008 Location: Bereldange, Luxembourg Posts: 41	In order to clarify the 80% I will explain my 80% a bit more (as I am writing software, I look it at more on the digital side than on the analog one which might sometimes be a fault). 16 bit audio normally is stored as signed integer going from −32768 to +32767. By 80% I just wanted to tell that in my case, it was going from -26000 to +26000 so there has been room left from the sampling point of view. Sometimes distortion is introduced due to the loudest point being beyond 32767 and the waveform is simply cut. But as here it wasn't touching the 32767 by margin the distortion seems to have occurred in analog circuits prior to sampling. Nevertheless I told the operator that I never again want to see him without headphones.

September 8th, 2009, 06:27 AM	#7
Rob Morse Major Player Join Date: Feb 2009 Location: Charlotte, NC Posts: 427	David, if the guy wasn't wearing headphones then there isn't much to talk about. It sounds like the guy you were using was inexperienced and I would attribute it to something he did. It sounds like the mic was overloaded and he never would have known. I did this once myself, years ago and it's the best way to learn. As Don mentioned, you can play with it in post but good luck with that. It would be the same as trying to fix video that had the gain turned up all the way. By the way, the Z5 has a trim adjustment so I would imagine the Z7 does as well. I also have found Sony's to be a little hot on the audio and since I shoot in places with loud music, I set the trim to -6 db and it's worked out. Recently, I started using a Shure SM57 in a wireless setup (along with my usual AT835). I stick it on a mic stand by the DJ speakers. I can honestly say it has made a huge difference when shooting in that environment. The mic can handle the noise and I can move all over the room and keep consistent audio

September 9th, 2009, 04:43 AM	#9
David Arendt Regular Crew Join Date: Aug 2008 Location: Bereldange, Luxembourg Posts: 41	The wireless transmitter was connected but ignored as I had the Rec CH switch to CH1,CH2 so the same signal from the on camera mic was recorded on CH1 and CH2. This is exactly what I don't quite understand. CH1 which was on AUTO and CH2 which was on manual where receiving the signal from the same microphone. However on the AUTO channel which was sometimes maxed out, there was a lot less distortion than on the MANUAL which has not been maxed out.