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GH2 Audio Hacks
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  • @andyharris have you had success in getting a remote to work with an external mike plugged in with your custom made cable?

  • Didn't see it in the thread, but has anyone experimented with using an attenuator and the VMP with +20 db on?

  • @evero @konjow @rambo

    I have not tested for the presence or absence of resampling on Vimeo yet since I often downsample to 44.1 KHz or use a Redbook master (in the case of music videos) before uploading. But the official page on audio specifications for the Vimeo site very strongly suggests that they resample to 44.1 KHz if you upload a higer sample rate.

    The easiest way to test this is to use an application like your professional sound card`s software mixer (or a dedicated application like HiJack Audio or Virtual Audio Cable) to route the output from your Vimeo playback to your favorite audio recording application and record the results (to analyze later) or analyze them on the spot.

    To accurately test this you will need to ensure 2 things.

    1) That the audio file you uploaded (in the form you uploaded it) contains material above 22.05 KHz that you can easily discern with your analysis software.

    2) That youraudio interface and software are setup to playback at your intended sample rate when you are recording the output from Vimeo.

    If the frequencies above 22.05 KHz have disappeared after upload in the Vimeo playback, you know that they have resampled to 44.1 KHz or lower. Incidentally, as of 2010, MySpace was resampling to 22.05 KHz for their playback, so you lost everything above 11.025 KHz. I do not know if they still engage in this approach because it really turned me off.

    Anyway, if you want to know more about resampling, the best resource on the net is currently infinitewave.src, but if we want to discuss the topic more we should setup a dedicated thread. :)

  • I've been working with the audio patch for a few days now, doing interviews, using external mixer. It seems like the two first settings are clipped digitally even though the meters do not hit the 0 dBFs mark (both in camera as in editing).

    My first conclusion is that the mic level 1 setting (AGC 0 set to 203) has a -12 dB attenuation after it has been digitised. The mic level 2 setting (AGC 1 set to 176) has a -5 dB attenuation after the fact. Does that sound familiar to you guys?

    The problem is that my mixer's output (sounddevices 302) only goes down to -56 dB mic level, which seems to be 6 dB too loud for the input of the GH2.

  • @DirkVoorHoeve Here is what I found during testing.

    • The GH2 can clip at the input stage when using an external mic without exceeding the meters.

    • My memory is camera can exceed -12 dBFS at Mic Level 1 when it is being fed a proper signal, but be aware that with most of the settings there is still some AGC kicking in (such as compression) if you get too far up (e.g. - 3 dbFS with an external, etc.). Your better bet on this is to check what earlier comments were made on the topic as others did various testing with mixers, while none of my testing used that particular source.

    • The AGC processing is much less noticeable in the top part of the dynamic range with the internal mic than with an external mic. For some reason the camera handles it differently.

    • The best way to get a good dynamic range with the camera when using external devices is too make sure they do not clip at the input stage (like +20dB setting on the Rode VMP will) and to try to make use of a low noisefloor. If you use that in conjunction with Mic Level 1, you should get a good dynamic range.

  • Just returned from B&H today...where again and again the folks recommended to use separate audio recording, since the circuitry in the cameras is not A plus. And whatever the circuit does...the compression is worse. I have a small Tascam recorder where I record separate audio while shooting, and the recorded wav file will always sound a hundred times better than anything through my matter what patch/hack!

  • @mppohl That seems like a random comment. :) Practically everyone here has already said that using a 2nd system recording can give higher fidelity and that uncompressed audio is preferred to 192 kbps AAC.

    The point of the hacked settings is not to have the best sound quality that is at all possible. The point is to have the best quality you can get without any chance of sync issues or without any additional equipment.

    Now, many other cameras can record uncompressed audio (BMCC, RED, etc.) while the GH2 does not. What the GH2 does have is a surprisingly decent pre and A/D combo for the money. If you listen to hacked GH2 audio using the internal mic vs any of the other DSLRs before it, you can hear the step forward.

    The GH2 audio is MUCH better than 5DMkII, 7D, GH1, etc. The dynamic range is pretty decent. I have not compared it to more recent DSLRs. But once again, it lags behind the ones that support uncompressed audio.

    If you want to go with 2nd system sound, the possible sonic quality you can attain can be much better. No one here was trying to say otherwise.

    Just make an effort to get good equipment, because you can also make it worse if you make the wrong choices. But the highest potential sound definitely comes from 2nd system. But there have been no reported incidents of lost or out-of-sync audio on the GH2 that I have heard so far with the internal ones.

    If you have the manpower for 2nd system (and to make sure that it is properly recording the whole time and sync afterward) there is literally no reason not to go for that.

  • @thepalalias do you know why it clips without exceeding the meters? do you think it is clipping of the pre-amp or is it digital distortion?

    For now i've settled with mic level 2 (AGC 1 set to 176) and the limiter of my mixer at -12 dBFs.

  • @DirkVoorhoeve It is not entirely clear whether the distortion comes from the pre-amp stage or the subsequent A/D, but it is clear that by the time it hits digital, it has been destroyed.

    My best guess is that it is an issue with the voltage hitting the pre and everything cascading from there. However, since we have no manual control of anything between the input into the pre and the time it comes out of the A/D, I am not really analyzing that aspect.

    Hopefully things will be simpler on the GH3. Glad that your current workaround is good enough for the moment. :)

  • So said T R R S 2.5 MM plug came with RCA plugs ... I could not get the camera to see external mics ... I am still thinking about where I went wrong...

    Maybe there is some sort of dongle arrangement ... or resistance...

    I made some tests with the Zoom H4n and the prebuilt cable... only one channel seemed to work as well...

    Has anyone gotten two clean channels of audio to work using any plug? What plug?

  • Here it is... it is tip ring ring for the audio... tip ring and the ground is ring...

    See this picture

  • @LALisa I have a vague memory that I got it to work without any additional steps - I will try and dig up the documentation.

  • @thepalalias any improvement or news about the beta 2 to final hack for the Audio. Its still in beta 2 master... ;)

  • @rajamalik What we need is for someone to adjust AGC values for AGC Setting 0 and AGC Setting 3 by 1 at a time using a consistent reproducible external sound-source and then upload them.

    There maybe room to squeak out a tenth of a decibel or so in either direction for both.

    But the question is whether the work is warranted. The beta is pretty close to where we can go. :)

    If people want to help test this, I can provide FTP access.

  • @thepalalias i really love to test this but i need the basics what you did to reach beta. i am in very basic if it comes to audio hack. send me details and the improvement analysis excel sheet so that i can easily go through the development and test out some new co-ordinates.

  • @rajamalik Okay, I will see what I can do. :)

  • Just a note for anyone that has not had a chance to sort through the GH3 specifications yet.

    • The GH3 has new 3.5mm input audio jack and 3.5mm headphone jack. There is still a 2.5mm port but it is now only used for shutter cables, etc.
    • The highest quality is now done in an MOV container and audio is apparently uncompressed linear PCM. The samplerate and bit-depth have not been mentioned yet but 48 KHz, 16-bit seems most likely.
    • There has not been any official mention of any XLR add-on at this point.
    • The menu screenshots shown so far confirm similar meters (8 bars) and gain control (4 bars) to the GH2. No word on whether AGC is still in play or in what fashion, but it would not surprising to find it handled similarly in the firmware. Much too early to tell.
    • No word on whether the ability to modify audio levels during recording has been added.
  • @mppohl Check page 6 from this thread. Three very short clips of a drum, taken from a CD via a field mixer into the gh2, so no mic in the way. You will hear no difference. We found out that the limiting - circuitry of the field mixer affected the sound more than the GH2´s circuitry. The preamp and D/A stage of the GH2 are sufficient, and I also record with 384kbs, same rate the XH-A1 HDV cam used. Nevertheless, I use ecternal recording gear, but only for ambient recordings or when protagonists are plugged to a lavalier. I wanted to use a wireless first between GH2 and lavalier first, but with a lavalier plugged to a small recorder there are no hassles with transmitter frequencies, especially when travelling a lot. But you´ll have a lot of work in post

  • @thepalalias I'm currently using Apocalypse Now Boom v1 by Driftwood. Does that mean I automatically have the audio hack/setting included when I use Apocalypse Now Boom? Although I record actors with separate sound, I often find good background sounds from what the GH2 records. So my question is - assuming the audio hack is already included, do I need to adjust any settings to get the best sound from the GH2's built-in microphone? Thanks.

  • @matt_gh2 Yes, that setting already includes the audio settings I assembled. All you need to do is pick the Mic level that best suits you. :)

  • @thepalalias Great - thanks for you excellent work.

  • Hi, everybody! Tell please, somebody can knows, impedance of a microphone input at GH2?

  • @aenima No one has posted a definitive answer yet. There was some discussion of it back in August when @LALisa was doing some testing.

    You can find her notes in the thread at these two links.

  • Thank you thepalalias. In that case we will try to measure it on these days off. I think it can be useful.

  • I hope to someone it can be useful. On measurements, impedance of a GH2 microphone input is equal 4.7kOm