TriCaster’s analog audio conforms to SMPTE RP-155, as apposed to the EBU standard. The maximum input/output level is +24 dBu. Nominal input level is +4 dBu (-20dBFS), and the sample rate is 96 kHz. Levels above 0dBVU are shown in red in the VU meters, to caution you that overly high levels can result in clipping in recordings.
If you need to calibrate the system for EBU referencing, you’ll need to take the difference between SMPTE and EBU levels into account. A small adjustment to the TriCaster’s audio mixer will allow you to achieve this and therefore maintain a constant audio level from input to output.
Audio Headroom & Clipping
In digital audio systems, signal levels that exceed maximum values are uniformly assigned the maximum value, a condition known as “clipping”. Clipping inevitably results in annoying audible issues. Worse, over-modulation that may not be apparent while listening during live production may nonetheless appear in recorded files. This is often true even when levels appear to be below the ceiling level (0dBFS, the maximum allowable digital level). For this reason, it’s customary to configure normal operating level (also referred to as the ‘alignment level’, and sometimes, ‘nominal level’) well below the clipping limit – sufficiently so that occasional excessively loud sounds (say, loud laughter or applause) can be accommodated without risk. This range between nominal level and the highest possible level is commonly referred to as ‘audio headroom’.
What is considered a suitable headroom allowance can vary from one locale to another, in different industry applications, and even in individual studios. Headroom levels between 18 and 24dB are not uncommon in professional digital audio realms. TriCaster allows for any preference in this regard, by its provision of separate Record (and Stream) level controls. For example, dropping the Record slider to -20dBFS (our base recommendation, by the way) approximates typical professional practice. This has no impact on levels at TriCaster’s audio outputs, but all but ensures clipping in recorded files will be avoided. You can therefore record files conforming to regional standards or personal preference, substantially reduce the possibility of audio clipping in recorded files and even adjust the level on the fly if necessary.
Audio Levels & Scales
Differences in VU scales can also cause confusion. A reference signal registering 0dB on a 'dBVU' scale could register -18db on a 'dBFS' scale depending on calibration, although the actual audio is no different. Scales can vary between different software and hardware which is why TriCaster allows you to choose dBVU, dBFS or dBu.
Therefore, if when you bring your TriCaster recordings into your non-linear editor the levels are too low, you can reduce the amount of audio headroom by simply increasing the record level using TriCaster's audio mixer record fader control.
In regards to the clips recorded on the Tricaster, NewTek record audio with 20dB of headroom (the pro specifications) and so when you play a file (that has been recorded) back NewTek apply a corresponding +20dB of boost so that the exact level it was recorded at is also played back. NewTek do not do this with files where the reference level is not known (which is normally normalized files, or 0dB of headroom) or they would all play back way too loud.
A Simple Audio Test
In order to help with troubleshooting, this test should show that audio levels between TriCaster and any Editing software are aligned and any discrepancy is most likely because of the difference in audio scales or caused by other additional devices adding some boost on the way (eg. encoders, converters etc.).
- Import the sample 1kHz test tone into the TC’s sound media player, turn on loop and start playback
- Set the TC’s audio mixer scale to dBFS
- The TC’s audio mixer should report an audio level of -20
- Record a few seconds of playback
- Exit to Windows and transfer the recording to your Adobe Premiere/FCP workstation
- Import the TC’s recording, drag it to the timeline and start playback
- Premiere should report the same -20 audio level