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    CX350 and Auto Audio Levels (not with Limiter)
    #1
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    Hello,

    I am getting to know the CX350 and the auto audio levels seem to be lower than I would expect. They seem to be tied to the headroom number. So if I have the headroom set to 18dB the levels peak at 18 dB. On the PX270 the auto audio levels would peak at a higher level outside of the headroom adjustment yielding a stronger audio track. I find with the CX350 the audio level is very low for the auto track.

    For example, I use Peluso condenser mics and they are relatively hot. On the PX270 I have the mic attenuation at -40 dB and the audio levels have always been fairly full when I bring them into my NLE. (headroom at -18 dB). On the CX350 I need to run the mic attenuation at -50 DB and the auto levels are still kind of low.

    Am I missing a setting or something?

    Thanks.


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    #2
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    Yes, this mostly matches my experience, although I don't really use Auto levels for audio much as it's rare for any camera to correctly identify what audio you actually want to record and what the correct level should be. And as a result auto level control often ends up boosting the volume on sections of audio that should be quiet.

    If you set the audio levels to Manual rather than Auto, are you able to adjust the level to get a decent record volume?


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    #3
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    Ok, I did a little with a mic plugged in to channel 1. I set both inputs to read from the mic and put one on manual and one on auto. The manual gain was set to 5.

    In this scenario, the two levels were the same. I was able to turn up the gain to at about 12dB at the max.

    What also is of note is that the level is dependent upon the "headroom" setting. So in my test with a mic about six inches away and speaking in a normal to low talking voice, the level peaked at the headroom setting. So when the headroom was set to 12dB the levels were -12dB. When the headroom was set to 18dB the levels peaked at -18dB.

    On the PX270 the results were the same EXCEPT, the auto channel always peaked at about -8dB or -6dB regardless of the headroom setting. So the auto levels setting was set to give you a full audio track that was ready to go if you did not boost in post. So I guess what I am seeing is that the auto audio levels on the CX350 are very conservative. Imho too conservative as who is going to track at -18dB? Way too little signal being recorded. I use auto for sporting events and other general uses but go to manual when it counts. So it serves a role but it needs to be a finished working level to be useful otherwise your audio track is way to low to deliver.

    Barry or Mitch, can you find out if this was a choice and can it be altered back to the PX270 approach? Thanks.


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    #4
    Senior Member Mike Warren's Avatar
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    Quote Originally Posted by Bassman2003 View Post
    On the PX270 the results were the same EXCEPT, the auto channel always peaked at about -8dB or -6dB regardless of the headroom setting.
    That sounds to me like a bug in the PX270. Headroom should, IMO shift the "0" point down by by whatever you set the headroom to. It's not possible to add more to the top end as 0dBFS is all bits full.

    Does the CX350 record in 24 bit? If so, then you won't lose any quality by boosting the signal back up in post.


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    #5
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    When recording MOV on the CX350, the audio format should be 48 kHz @ 24-bit LPCM. When recording AVCHD, the audio format is 16-bit (48 kHz).

    Note that 20dB and 18dB of headroom are fairly common for broadcast purposes. Since digital audio generally has a hard clip at 0 dBFS, a reference level of -20 dBFS (according to the SMPTE standard generally followed in the US) or -18 dBFS (according to the EBU standard used in Europe) allows a decent amount of headroom before clipping. Peak audio levels would generally be above the reference level, but still below the 0 dBFS clip point:
    https://www.soundonsound.com/sound-a...-audio-systems

    Interestingly, the CX350 manual has this to say about the HEAD ROOM setting in the menu:

    • [20dB]: Select this when matching the recording standard level with the Panasonic broadcasting AJ series camera.
    • [12dB]: Select this when matching the recording standard level with the Panasonic professional AG-UX series camera.

    Beyond the headroom setting, it sounds like there could be a difference in the auto level behavior between the different cameras though.


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