Australian Sound Artist

Saturday, May 10, 2014

Hydrophone Test #2

:: Hydrophone cable connected to Neutrik NA2MBNC adapter ::
The part 'B' of an earlier test I did with the Teledyne Reson TC 4033 hydrophones. Again - long overdue but well worth the wait. As a quick recap - the first test entailed doing a small series of recordings with the hydrophones in a controlled environment (my bathtub), using Raimund Specht of Avisoft's preamps #42003, recording onto my trusty Sound Devices. I won't go into more detail as if you want to know more tech specs etc. please have a look at the original blog entry - it's all in there!

For these final test-recordings I set-up exactly as per Test #1, with the only variable being the exchange of the #42003 preamps for 2 x Neutrik NA2MBNC adapters (see image above) and the input gain db's. Water was at the same level/temperature. The sounds I recorded  entailed pouring water into the bathtub using the same jug and with the exact same technique as last time. Ideally, I would have done these tests using four inputs and the two setups - recording simultaneously each event as it occurred but this was not possible purely because of gear access. I was lucky enough to have two of the hydrophones but not four.... The next best method would have been to record both tests one after the other, with no delay in-between - but unfortunately I did not have the adapters at the time of the first test - nor did I know that I would want to further explore the hydrophone's sound quality in this method - not until I had completed Test #1. So here we are with the next best thing - me attempting to mimic in every way - the original methods the only (conscious) variables being the controlled gain level on the 788T and the preamp-swapped-for-adapter. 

Hope this makes sense......

After Test #1 I was concerned with a slight humm that was coming through on my recordings - particularly when the input gain was above 38db. After assuming it was from the preamp, I decided to try the recordings with a simple adapter and compare the two results. I knew from the off-set that gain levels on the 788T would need to be a lot higher - ultimately driving their preamps a lot harder. You could say I was really testing the preamps.... Avisoft Vs Sound Devices....

Key differences between the preamps and the adapters include the fact that unlike the preamps, the adapters do not have a high-pass cutoff controlled by a rotary pot, nor do they amplify the sound in any way. Their function is purely as a port adapter, from BNC to XLR so as to connect into the recording device. By using a simple adapter (as opposed to a cable) not only is it most likely cheaper, but it retains the quality of the signal conducted by the high-quality hydrophone cable - right up to the recording device.

All were recorded one following the other, in the exact same conditions with the only variable between them being the gain on the 788T. You'll notice that the starting gain level is 20db more, than Test #1... Other than converting files to MP3 @ 320kbps for the audio players I have left them completely untouched.

Gain: 54.7

Gain: 58

Gain: 62

Gain: 66.4

Gain: 68.5

SUMMARY: The sound quality facilitated by the Avisoft preamps becomes abundantly clear when comparing the recording results. These preamps ensure that the delicate details of low frequencies are well presented and preserved as can be best experienced when listening to the bubbles rising through the water. The general recording level is also quite adequate. Louder levels are possible but with the compromise of the humm (this may be able to be reduced in post-record editing). In comparison - using only the adapters acted almost as a lowcut at around 160Hz. In addition to this loss of lower frequencies the general level of the recorded sound was well below what the 788T's preamps could managed to successfully boost without a noticeable and destructive hiss of noise interference coming through. Even when keeping the 788T's gain at low levels so as to try to avoid increasing the noise floor, the recorded sound was almost too low to be useful. I will say that the higher frequencies of the recordings that were gathered using the adapters (as opposed to the preamps) were noticeably more crisp - but still - just too low. If I was recording very loud sounds of the range >700hz then the adapter-setup might suffice.... Ideally though - I would suggest the TC 4033 teamed with Raimund Specht's #42003 preamps - which I have a new level of respect for.

THANKS: To the helpful people of Teledyne Reson - particularly Tom Mortensen and Brian Burge who so patiently answered all my questions. To Raimund Specht of Avisoft for taking the time to put together such useful pieces of speciality recording equipment and again - for helping me nut out all my answers...