Multibridge Extreme – Distorted audio on embedded HD-SDI Audio

[Luke Maslen]

Hi Daniel,

I don’t have one of these displays and so can’t test it. It would be very helpful if you could run the following tests:

1. Try monitoring any of the audio outputs of Multibridge Extreme while playing out HD video, eg monitor the RCA analog outputs. Can you hear any distortion? The analog and AES audio outputs are de-embedded from the SDI-embedded audio and so if there is distortion on the SDI audio, there should also be distortion on the other audio outputs. If you find no distortion on the other audio outputs, then that would suggest a problem with how the LCD display is handling the embedded audio of the HD-SDI signal.

2. Quit out of all applications and ensure that your Mac OS X desktop is showing on the Panasonic BT-LH2600W display. Open the System Prefences and click on Sound. Set the Output to DeckLink Audio.

While in the System Preferences, click on Displays and enable the Show displays in menu bar option. Quit from System Preferences. Now go to the Displays menu and set the Number of recent items to 10.

From the Displays menu, change the Television resolution to an SD setting such as 720 x 486, 29 Hz (NTSC). Launch iTunes and start playing some music. Does this sound OK through the Panasonic BT-LH2600W? Assuming that it does, keep playing music and switch to 720 x 576, 25 Hz (PAL). Note whether the audio from the Panasonic BT-LH2600W is clean or distorted. Continue to work through the various 1280 x 720 (HDTV 720) settings and the 1920 x 1080 (HDTV 1080) settings and note whether the audio is clean or distorted for each setting. Are there any resolutions or frame rates at which the display will not correctly display video? If so, how does the audio sound when you select these troublesome video settings.

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Please let me know what you find for tests 1 and 2.

Regards,

Luke Maslen
Blackmagic Design

[Danieln]

Luke –

Just an initial note. The monitor correctly handles HD-SDI video/audio directly from a Varicam. No audio distortion.

ANSWERS TO YOUR TESTS:

1. The audio output from the RCA monitor jacks is fine all of the time. When outputting HD video, the HD-SDI audio is distorted, the RCA audio output is fine. Switching to SD-SDI, audio is fine on both the RCA and SDI.

2. From the desktop using Itunes as an audio source: The monitor would display all frame rates except for 2K settings. Up to this point, I had only tried outputting HD at 1280×720 (as I have 720P source footage). When I switched to any SD or 1080 output setting, the monitor would display correctly and the SDI audio was fine. The analog audio was fine at all frame rates and settings. Changing the display settings had no effect on the RCA outputs or the XLR outputs. So this appears to be an issue with just 720P HD over SDI. Again, I used this monitor with a Varicam at 720P and the audio was just fine. I don’t have another SDI monitoring device at the moment to perform additional tests, but it would appear that the issue is with the 1280×720 output settings.

Thoughts?

[Luke Maslen]

Hi Daniel,

Thank you for posting the results of your testing. You mentioned you have a “Varicam” and I’m hoping that means you have a Varicam deck rather than a camera. Assuming you have the deck, would you please conduct the following tests?

Test 1a
Use Final Cut Pro to output 720p59.94 via the Channel A HD-SDI output of Multibridge Extreme to the HD-SDI input of your Varicam deck.
Please monitor the audio at both stages, ie:

[Luke Maslen]

Hi Daniel,

Please let me know your findings when you can as I am keen to find out where the problem lies.

Regards,

Luke Maslen
Blackmagic Design