Audio Popping/ Cracking???

[vmkeow]

What are the specs of the audio section? Is it posted anywhere?
Is there a block diagram or flow chart of audio signal chain? This could reveal a poor design.
Are there cheap components in place causing poor audio? Sometimes companies want to save a few pennies at the cost of poor audio.

 

[TheMusician]

Is the audio mic/chain the same on the HMC150 and the HPX170?

 

[ullanta]

We don't have access to the internals of the HMC audio system, or specs. We don't know if it's the same as the 170.

Long ago, there was a project here on DVXUser to replace the mics on the HVX with an input for 2 more external mics. They went far beyond what most of us would be willing to do to our cameras to find info - but still didn't get too deep into the audio electronics - and what they did find was hard to understand! (there were 4 internal mics, not two, that seemed to be blended in a very strange way; see http://www.dvxuser.com/V6/showthread.php?t=70971)...

So... don't hold out too much hope about learning details of the HMC audio system....

But we can intuit, from experimentation, some of it, as I have above.

 

[vmkeow]

I think companies deliberately shield us from detailed specs on their cameras audio section because if they revealed them, we would see how poorly/cheaply designed they really are. So, keep it a secret and discover it after the fact for yourself(?).

 

[SPrimeau]

Actually, this is not the case. It is obviously a mismatch of the output level of the mic and the headroom of some stage of the camera's mic inputs.

First, the kind of distortion we're hearing doesn't sound like mic distortion, it sounds like clipping. The sounds are distinct.

Second, you can't tell where the distortion is without more information. Is it the capsule itself incapable of handling the SPL? Is it that the mic electronics can't handle the signal level the capsule is outputting? Is it that the camera preamp can't handle the signal level coming out of the mic? Is it that the converters can't handle the signal level coming out of the preamp? Any of these - and more, which we just don't have enough detail about the HMC internals to suggest - can be the culprit when you hear distortion.

I would guess that the mics are not the problem in most of these cases, either internal mics or external mics. If human beings are in the same situation and not bleeding from the ears, mic distortion is not the most likely culprit. And, as I said, the sound doesn't sound like mic distrotion.

Since the problem occurs with internal mics, external mics, and external line-level sources, the problem can likely be attributed to an internal camera stage between the "boost from mic to line level" and the gain dials. The problem clearly comes before the gain dials, since lowering gain doesn't get rid of it.

A mic with low sensitivity helps not because the mic signal is distorted, but because it outputs a lower level signal than a higher-sensitivity mic in the same situation. This lower-level signal is less likely to cause this mystery internal component in the HMC to clip.

I know what is clipping and what is sound distortion. I also experienced sound clipping with the HMC (camera VU clipped and probably clipped digital mixer).

Yes, you said that we see the same thing with either the built in mic, an external mic and a line level from a mixer. I agree. But it doesn't fully means that it's only the camera the culprit. An external mic like a shotgun does have a limited SPL. And a mixer, especially a digital mixer will be prone to digital clipping. It can also be the camera VU that is peaking (sometimes).

Also, you said in a earlier post that you will test the HMC and other cameras like the HVX or the DVX. Do you have the results? To get a more accurate result, you should test both cameras at the same time in various situations.

Me, I think eventually I'll try to compare it with my DVX.

 

[wseng]

Just to confirm that I'm using the correct terms... Clipping means VU is touching 0db ? Distortion means some sounds like cracks or when u crumple or tear a paper sound effect but without the VU touching 0db ? Please let me know if i'm using the correct terms.

Me currently using DVX with internal mic and Rode NTG1 XLR. It occurs to me very often this paper cracks effects but most of the time the meter on my NLE or camera doesn't go full red, it reaches in the range of -3db to -6db.. That's what I see in my NLE and also Adobe Audition. With my current situation I'm already doing many audio restoration works to correct the audio. In my wedding culture, there's always loud screaming of toasting and guys screaming in the games before picking up the bride. Sometimes even when I'm not near the speaker and my VU level is around -18db. The internal mic would get this 'distortion' too.

If I were to get the HMC ? Ullanta, were saying that it will get worse than my DVX ? with even more post audio restorations to do ? Would the ATT pad effectively correct it ? or prevent it? How if I need the internal mic for ambience sound which I normally include for my full footage that I pass to my customers ? Any method to stick an ATT pad for the internal ?

Really frustrating thinking so many good things on this HMC .. and only I bad thing that I can't tolerate - correcting the audio.

 

[ullanta]

Just to confirm that I'm using the correct terms... Clipping means VU is touching 0db ? Distortion means some sounds like cracks or when u crumple or tear a paper sound effect but without the VU touching 0db ? Please let me know if i'm using the correct terms.

Technically, "distortion" is any difference between what is recorded and a perfect representation of the real-world sound - EQ is a form of "distortion", etc/ But in common use, it means unwanted sounds introduced by problems with the audio equipment.

"Clipping" is a kind of distortion when a signal is too strong for a device to handle. "Digital clipping" is when a signal is too strong to be represented as digital data (VU meter reaches 0dBFS).

I was comparing mic capsule distortion - introduced when the physical sound is too loud for the microphone capsule to handle - to clipping distortion. Mic capsule distortion tends to have significant low-frequency components, while clipping tends to have a square-wave sound and mainly high-frequency components.

It's hard to tell without hearing samples what you're experiencing. If there are screams very close to the mic (internal or external), it's possible the capsule is overloaded, and only a different mic might help. But it may also be that the DVX/HMC preamp is being overloaded, in which case a pad might help. In my experience, the HMC preamp overloads at a pretty low level, while few mics will truly overload at sound levels that don't cause a person severe pain. So, for the Rode, I'd try out an attenuator, and I think it might solve the problem. For the built-in mic, there's of course no easy way to add an attenuator... though I suppose you could crack the camera open and try...

If it's a real and frequent problem, you could physically reduce the sound hitting the internal mic... this would help with very loud sounds, but would of course make the mic less sensitive to sound in general.

Keep in mind... the ONLY clear comparison we have seen, from the Green Barry, indicates that the DVX was WORSE than the HMC in at least some situations. I plan to do some comparison myself soon. But for now, that's the best comparison result... we also don't know if this differs significantly between individual cameras.


Sound like pretty wild parties, though... do you have a video sample?

 

[TheMusician]

We don't have access to the internals of the HMC audio system, or specs. We don't know if it's the same as the 170.

I only ask about the HPX170 because the two cameras share the same glass, the same LCD, the same imaging block, the same body style except for the P2 slots on the back, and I just can't imagine Panasonic would use anything but the same audio mics/circuits for the two, and i haven't heard anything about audio issues with the HPX170.

This may be a question for Barry.

 

[wseng]

This is really weird.. just checked my footage. The distortion happens at volume levels of -12db and below from the internal mic.

Please check it out for me : http://www.d7weddings.com/download/Temp.wav

 

[Green Hornet]

It would seem that adding a mic pad would only reduce the output going to the pre amp stages creating a lower output overall which would require one to turn up the dials even more to obtain a desired audio level.

It seems as if the pre amp can not handle the quick rise from low to high.
This could happen if the pre amp output stages are few, if it only had say 8 stages of amplification instead of say 12, and each stage was made to do too much boost.

Some have suggest using a dynamic mic like an sm 57.
That would likely help, but the desired sound would contain too much of what is closest to you and not enough of the subject 5 feet from you.

I would think the only way to control this with out a fix would be to use a compressor between mic and camera to control the attacks in audio, that seem to overdirve the pre amp.

 

[ronedee]

Hey! I have, and have reported in detail on both real-world and controlled testing; the issues are clear. Some gain stages, likely after the mic "boost" and before the gain dials, are a little easy to overload. Solutions are clear, though not as convenient as some people may want.

-----------

I read your report.

But, did you us a live band situation? What mics (dynamic, shotgun, large/small capsule condensers)? What line levels, and what source (digital or analog mixers or recorders) ?. What settings on the various equipment?

If you look back at the beginning of this thread you will notice that I introduced all the SPL talk about condenser mics and analog to digital converters being suspect.

I also said, and believe that Panny won't do a damn thing about this problem unless we are well informed about it's nature.

"Extreme conditions" won't be a good excuse for them to do squat!

So, lets stop jawing the same sheet over and over again and get out there and figure this f*ker out!!

 

[ullanta]

It would seem that adding a mic pad would only reduce the output going to the pre amp stages creating a lower output overall which would require one to turn up the dials even more to obtain a desired audio level.

Right... but that's not necessarily a bad thing.

It seems as if the pre amp can not handle the quick rise from low to high.
This could happen if the pre amp output stages are few, if it only had say 8 stages of amplification instead of say 12, and each stage was made to do too much boost.

It's not an issue of discrete steps - EVERY preamp will clip at some point. In the specs of most preamps (but almost never on camera built-in preamps!) you'll see a measure of "input headroom", which is the strongest signal the preamp will accept before clipping. A great high-headroom preamp like the Millennia HV-3 has a headroom of about 23dBu; average for decent preamps seems to be about 16-18 dBu. The HMC seems to be towards the low end, but not outrageously so.

Some have suggest using a dynamic mic like an sm 57.
That would likely help, but the desired sound would contain too much of what is closest to you and not enough of the subject 5 feet from you.

I don't know how you get this - if you use the mic properly, and aim it properly, you'll get exactly what you want. A 57 is not quite as directional as a shotgun, but in the situations we're talking about, pinpoint directionality is not the goal (or achievable). But indeed an SM57 (or 58, more so) is a pretty directional mic compared to typical cardioids.

I would think the only way to control this with out a fix would be to use a compressor between mic and camera to control the attacks in audio, that seem to overdirve the pre amp.

A pad is better [in general] because it doesn't affect your dynamics the way a compressor or limiter does [though you might find some compression desireable in some situations]. But sure, many devices (such as the SD mixers) have what is called a "mic limiter" for safety, which will limit the signal from the mic before it hits the preamp.

Mind you, in the audio world, pads (attenuators) are common, and a part of every audio engineer's kit, and built into many microphones and preamps. Nothing strange about having to pad down the output of one piece of gear to avoid clipping the next piece of gear in the chain.

 

[Green Hornet]

ullanta, you are missing the point.

As for every amp clipping at some point (is this not obvious) ?
Preamps that have fewer stages tend to clip sooner, as each stage is required to do more.
You can't obtain nice headroom without good individual stages in the design.

About the SM57....
The only difference between a sm57 and an SM58 is the ball the 58 has, whereas the 57 has a tubular end. The 57 would look better than having a mic with a round ball on the end of your HMC150. As for directionality, if I am shooting a live band, I clearly would like some isolation from me in the crowd and the girl next to me talking about her boyfriend, and more of the band. Mic's pick up what is closest to them, picking up a mic with some sort of rejection to this is NICE!!!!!!

As to Pads, yeah I have pads, but that does not address the issue if it is caused by distortion of the mic pickup due to spl.

If the mic is sending a high output due to SPL distortion, and then the pre amp compounds this by amplifying the result. The output is the same with less amplitude, and hence that is in fact what it sounds like. Amplification of the harmonics, and not so much the signal untill clipping is heard. In fact you may be better off providing a hot input from a better mic, that can handle higher spl, so the pre amp stage does not have to work as hard. The line level is simply entering the stage post preamp so the preamp does not work as hard.

A good test of this theory would be to use a signal from something such as a ME66, that is a HOT MIC!


... It seems as if we have many here who want to make excuses instead of finding the truth.
I am not looking for band-aids, I am looking for fixes.

I can take any camcorder from walmart and film a live band and NOT have clipping at -6db.
Panasonic should be able to as well....period.

 

[ullanta]

As for every amp clipping at some point (is this not obvious) ?
Preamps that have fewer stages tend to clip sooner, as each stage is required to do more.
You can't obtain nice headroom without good individual stages in the design.

I'm not sure what exactly you mean by "stages" - but most top-quality, high-headroom preamps have few (1 or 2) gain stages.

As for directionality, if I am shooting a live band, I clearly would like some isolation from me in the crowd and the girl next to me talking about her boyfriend, and more of the band. Mic's pick up what is closest to them, picking up a mic with some sort of rejection to this is NICE!!!!!!

But no mic will help much in that situation. Even a shotgun near the camera will pick up the girl next to you preferentially to over something even 10 feet away. The only real way to address this problem is to get the mic (any mic) physically distant from the unwanted sound source. Directionality of any mic is a weaker effect than proximity, especially in the short range (< 10').

As to Pads, yeah I have pads, but that does not address the issue if it is caused by distortion of the mic pickup due to spl.

If the mic is sending a high output due to SPL distortion, and then the pre amp compounds this by amplifying the result. The output is the same with less amplitude, and hence that is in fact what it sounds like. Amplification of the harmonics, and not so much the signal untill clipping is heard. In fact you may be better off providing a hot input from a better mic, that can handle higher spl, so the pre amp stage does not have to work as hard. The line level is simply entering the stage post preamp so the preamp does not work as hard.

A good test of this theory would be to use a signal from something such as a ME66, that is a HOT MIC!

Right... and I've done that. I've used both test equipment and real-world sound to test the limits of the HMC inputs, so far only extensively with line inputs, and it's clear that the weakness is at some point before the gain pots. Given the reports here, and ,y own experience with mics, I'm making an educated guess that the problem with the HMC is not mic distortion, but clipping somewhere down the line between the mic and the gain pots.

... It seems as if we have many here who want to make excuses instead of finding the truth.
I am not looking for band-aids, I am looking for fixes.

Are you referring to me? I don't think that's fair. I'm actually analyzing the situation scientifically, perhaps too slowly for you, but thoroughly. I'm pretty sure I've narrowed down the range of suspect components in the system, which is exactly what must be done to identify the problem and figure out a fix. At the same time, I've given clear and useful advice on how to avoid the problem right now for those experiencing it. Your goal seems to be to make the problem sound as bad as possible so that Panasonic will acknowledge and fix it. Fine, I guess... but in the meantime, I'm shooting without any distortion and giving advice to anyone else who wants to do the same right now.

Cheers,
Barry

 

[ullanta]

I can take any camcorder from walmart and film a live band and NOT have clipping at -6db.
Panasonic should be able to as well....period.

A cheap camera from walmart also won't let you shut the iris down so that video is too dark or nonexistent, won't let you set manual audio gain that will have too low or too high a level, won't let you manual focus so that the picture is just a blur, won't let you do any of the things a professional camera will let you do to screw up your image and sound.

Does that make it better? I don't understand your point here...

 

[Jordan Berry]

A cheap camera from walmart also won't let you shut the iris down so that video is too dark or nonexistent, won't let you set manual audio gain that will have too low or too high a level, won't let you manual focus so that the picture is just a blur, won't let you do any of the things a professional camera will let you do to screw up your image and sound.

Does that make it better? I don't understand your point here...

His point is that the audio on a cheap camera can handle these conditions so why can't a $3,200 camera handle them.

 

[ullanta]

I understand that, it's just wrong. By the same token, why can a cheap radio shack dynamic handle SPLs that a $5,000 shotgun can't?

The HMC clearly isn't optimized for recording bands with its built-in mics. That doesn't mean it's bad. It's just not suited for that situation. The Walmart camera audio system probably has some drawbacks relative to the HMC in some situations, as well. Like, almost all situations.

 

[Barry_Green]

I understand that, it's just wrong. By the same token, why can a cheap radio shack dynamic handle SPLs that a $5,000 shotgun can't?

Exactly. Try recording an explosion with the $5,000 shotgun and you'll likely end up with a $5,000 stick.

If the mic on the HMC were a dynamic mic then yes, it'd probably be able to record louder sounds just fine. But then it wouldn't be nearly as sensitive as it is. On the DVX100B Panasonic juiced up the sensitivity to make the mic twice as loud as it was. That's gonna come off the high-volume end.

 

[Jordan Berry]

I understand that, it's just wrong. By the same token, why can a cheap radio shack dynamic handle SPLs that a $5,000 shotgun can't?

The HMC clearly isn't optimized for recording bands with its built-in mics. That doesn't mean it's bad. It's just not suited for that situation. The Walmart camera audio system probably has some drawbacks relative to the HMC in some situations, as well. Like, almost all situations.

I'm sorry... I wasn't specific enough so you didn't understand my point. I'm personally only concerned with the audio processing of the HMC-150. I don't care about the on camera mic, as I don't use it for anything serious. Some people will go out and buy a $80 iRiver and use it to record the audio from their external mics at wedding receptions. Why can't the HMC-150 contain the audio processing ability that an iRiver does?

I personally have yet to experience this audio clipping problem. But I haven't checked any of my reception footage yet

 

[ullanta]

I don't know about the iRiver, but many of the small recorders have pretty low headroom. I'd be surprised if the HMC didn't handle greater signal levels than the iRiver. However, the iRiver may indeed be less noisy... when I did testing in the past, I found that almost any cheap dedicated audio recording device available was less noisy than the DVX/HVX - just by virtue of the camera being an electrically noisy environment!

Jordan... seems like you're not having problems, likely because you're using appropriate and properly calibrated external equipment, no? Why get concerned because of some web discussion when you have real-world positive results? Sure, cover your bases and make sure... but it seems like the HMC works fine for you. The walmart camera likely wouldn't.

The Walmart camera likely has a stock low-quality audio chip with non-defeatable automatic gain; if it has a mic input at all, you have no control over the AGC so your sound will be pumping all the time. The overall quality likely will not be as good as the HMC. Assuming what has been said is true, it has one advantage - it will handle louder sound before distorting. The HMC has a much more complicated audio path, with multiple input options, a defeatable limiter, and likely higher quality preamps and converters. You have control over your audio, and better audio quality. It has enough settings that, with good external equipment, you can get a nice clean signal (as you do) from a wide variety of sources, likely a much cleaner signal at low levels than the Walmart camera. Effective dynamic range of the HMC is likely much greater than the Walmart camera. The HMC audio system is targeted at professionals who will likely be using external equipment, rather than at consumers who don't have high quality expectations but expect to take the camera anywhere and point and shoot. So, asking why the HMC can't do what the consumer cam can do is not useful.. it's not an apples-apples comparison. You may as well ask why the HMC doesn't pump up the audio gain whenever the sound level is low.