Lectrosonics SPDR Issue

[TimOneill]

Hello all,

 

I am a fairly contented owner of the Lectrosonics SPDR.

I front end it with a Sonosax M2D2 - an absolutely incredible piece of engineering.

 

Together I feel that they are the finest rig for ultimate portability.

Place it in a little backpack alongside a pair of DPA 4060's and there is nowhere that I cant record some top notch sound.

 

Alas, My little slice of paradise has encountered a perplexing (to me) technical issue.

 

Ive reached out to Lectrosonics Tech department but as of yet no reply - I guess they are swamped and will get back to me soon!?

 

Part of my work is involved in recording the sounds inside resonant structures. To do this I use LOM Geophones - another incredible instrument.

 

Lately, I  have noticed some consistent noise artifacts buried within my recordings. 

 

Im attaching a couple of examples of what i refer to in the hope that someone can chime in on what this might be caused by.

 

 

 

Considerations to note:

 

;; Ive tested the Sonosax and its clean.

;; Ive tested the Geophones and they are working fine

;; Ive swapped out cables - same issue

;; Im using the analog inputs on the Lectrosonics .

;; Im considering going Digital and feeding the Lectrosonics a AES3 signal but have yet to make the cable in order to test if the issue still arises. My thoughts are that this wuld bypass the SPDR Filter and compressor.

 

The files attached below lead me to believe that it is an issue caused by 2 things - Low "subsonic" Frequencies and the Amplitude of sound waves. Perhaps the Lectro SPDR just cannot handle Very Low Frequencies. Something that would make sense given the intended purpose of the unit isn't nessesarily using a Geophone!!

 

Any thoughts or advice would be amazing.

 

 

Thanks for your time. 

 

[The Documentary Sound Guy]

I have to admit, I don't have enough experience with your scenario to distinguish artefacts from intentional sounds.  Mostly, I hear what sounds like something moving around in the background and creating vibration that the Geophone is picking up, not anything I would consider a recording artefact.  Can you describe what you are hearing  (and aren't supposed to be hearing) a bit better?

 

I would test AES3 using your regular analogue cables.  No, they won't be AES spec, but they'll work just fine at short lengths (<50'), and with digital, they will either work or not — there's no chance of cables adding noise.

[TimOneill]

Fair point! 

 

**Headphone listening may be required**

 

You are correct in describing the situation - It is folks walking down a street and the Geophonee is attached to a Metal railing . Thus what we hear is the vibrational sounds of humans walking about.

 

What im after when recording in this scenario is the low end rumbles. 

 

What is not actually being captured is the intermittent pops and Hissing that is present on the recordings. It is almost as though the input is being overloaded through poor gain staging , although it most definitely was not. 

 

When I monitor through the Sonosax it sounds lovely and rich and the low end is pristine. 

 

To my ears, the Lectrosonic SPDR is "adding" what almost sounds like a poorly programmed Gate or compressor?

 

I'm trying to figure out if the machine is defective or perhaps the Lectrosonic SPDR just isnt meant to handle very low end frequencies...

 

The sound I attach below here might highlight this more clearly - its almost like a "morse code" of static and pops lives on the recording ? 

 

 

 

Cheers for the tip on the AES cable - good to know. 

 

**Headphone listening may be required**

 

[r.paterson]

Are you feeding it via aes? 

There was an issue with aes in SPDR clipping, but that may have been resolved with SPDR firmware up dates?. 

[TimOneill]

10 hours ago, r.paterson said:

Are you feeding it via aes? 

There was an issue with aes in SPDR clipping, but that may have been resolved with SPDR firmware up dates?. 

No - I was considering using the Digital Inputs and actually hoping that may help resolve the issue...Yikes, your saying it may actually be worse then? 

 

I am thinking that the extremely low frequencies that are part of Geophone pickup might be overloading the front end of the SPDR ?

 

I was well aware when I bought the unit that it has a 35Hz filter "hardwired" into the Analogue Inputs signal path .

 

My plan was always to go Digital as I thought that might open up the low end and bypass any of the Lectrosonics "colouring" the signal chain .

 

After all the unit is basically designed for Dialogue capture in challenging circumstances - not Subsonic Frequency capture!!

 

Now, if only Lectrosonics would respond to my query.

[mlohninger]

I have nothing to add, but will note that it's thanksgiving in the US, and many companies are closed.

 

[karlw]

Hi Tim, yes, we were closed last Thursday and Friday, which may delay our response if you sent us a message any time from mid-week on. 

 

I've sent a link to this thread to our engineering team, and they mentioned that the recordings you posted don't have the SPDR headers in them, and we'd like to get those original recordings if possible. Please PM me a link to a filesharing location if you don't mind setting that up. 

 

Also, if there's a way you can set up a test where the same transducer is feeding both an SPDR and also a different recording device, we'd love to get the two recordings for comparison. 

[pscottm]

I would bypass all analog stages which follow the M2D2 and use its AES output into the SPDR.  I also use an M2D2 and find that much of the magic is in the Sonosax AD conversion, not just the preamps.  To forego the Sonosax conversion in favor of the Lectro conversion is borderline travesty, though I'm sure the SPDR ADC is not bad, just little chance it can compete w the Sonosax ADC, one of the finest you'll find anywhere, utilizing dual ADC's per channel and giving 135db dynamic range (vs 110db of SPDR).  For the nuanced sounds you are exploring, or anything else, go AES!  Not only will the noise likely disappear, you will gain depth of sound you didn't know you were missing.