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02-22-2013, 10:53 AM   #1
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K-30 Synching 32khz audio with external audio capture devices at other sample rate

Hello,
I am in final process of evaluating K-30 for purchase, but one audio issue remains unclear to me. As I realize that the K30 does not have an external microphone jack my intentions are to capture audio with an external solid state device. I have Sony PCM-M10 and Tascam DR-07. These devices record at various sample rates and formats but none match precisely the K30 audio which is encoded in camera at 32khz.

When I go to synch up the external audio recorded at say 48khz will the K30 video file remain in synch given all other parameters such as length clip length are identical? Is is necessary to first extract the 32khz audio from the K30 clip and convert it to 48khz to synch it with the externally recorded audio before decoupling the superior audio with the video clip?

Does the 32khz sample rate of the K30 audio represent any challenges to synching 48khz external audio. For landscape shots and nature clips, synch is not so bad if it is off, but speech and movement that visually triggers anticipated sound like a closing door looks ridiculous if the movement does not match.

I have studied the relationship of synching various sample rates on other sites, but none have been Pentax K30 specific.

Does anyone have any experience with synching K30 audio with superior externally obtained audio?

Thanks,

02-22-2013, 11:11 AM   #2
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I don't see why the quality of the audio would make a difference. If possible use a clap board to help with this. As long as you can see / hear the spike in the waveform you should e able to sync it no problem?
02-22-2013, 05:30 PM   #3
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The clapperboard is a great idea. That is the way that I have synched video camera audio and external audio in the past. However, then my video camera actually recorded its audio at 48khz and the external device also recorded at 48khz. Therefore as long as my initial clapper slate or hand clap were synched I would have no problems. Even a final clap or slate at the end of the clip would align perfectly. When external audio was overlaid on camera audio there was no echo effect either, so when I substituted the external audio into the camera clip everything sounded right.

The fact that the K30 internal audio is 32khz and my planned external audio will be at 48khz (from digital recorder with lav mic or stereo pair mic) I anticipate a synching problem. I was wondering if others have encountered a problem with substituting 48khz or 44.1khz audio onto the video track.

Today I conducted the following experiment: I recorded a video speech clip on a Canon video camera that recorded 48khz audio. I then re sampled the audio down to 32khz ( Audacity) and reassembled the clip in Sony Vegas. The clip now was at 30fps standard definition with audio at 32khz. Presumably this could represent a theoretical output of a typical K30 clip. I played the clip in several media players to determine if everything read 32khz. It did.

Using audio that I recorded simultaneously on a Sony PCM-M10 digital recorder (@ 48khz) and Tascam Stereo mic, I synced the beginning slate (handclap) into the clip (Sony Vegas). After approximately 2.5 minutes into a 4 minute clip, the audio began to misalign to the point where an echo became apparent. I zoomed in on the WAVE forms that are displayed in the track and sure enough the alignment started to shift. At the final clap at 4 minute end, visually the clap on the video was spot on for the 32khz audio clip that originated from the resampling, but the superior sounding external audio had slipped to a point where although it showed proper alignment in the beginning at 4 minutes the clap was preceding the sound enough to distract. After perhaps a 10 minute clip, the effect would truly be obvious enough for even a very casual viewer.

So my conclusion is that perhaps an external recorder using 48khz quality will synch with the K30 audio as easily as any camera's audio at the clip's start, but by 2-3 minutes into the clip the alignment would require tweaking to keep the external audio optically paired to what one sees on the screen.

Any suggestions from K30 owners on potential problems with pairing with external audio capture? Since my Kodak ZI-10 bloggie cam records at 48khz, it is really disappointing that Pentax choose to use 32khz capture with no external input. I have many old M42 lenses that I would love to use with video mode of K30 as I do with my K10 for stills, but possible audio synching headaches are causing me to wonder if using the old glass if worth the forfeiting of optimal audio utilization.

Thanks in advance for suggestions.
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