Noise, me66/k6, LS11 and audacity. (1 Viewer)

I recorded the noise at night in silence, at different attenuation levels, from the setup me66/k6 and ls11 and used the noise recordings to reduce noise from actual recordings made at approximately the same level. It worked ok. When using noise recorded at higher level than the level used in the actual recording it didn't work that great. It showed by eye as vertical lines on the "waterfall" spectrograms. Don't over do it.

Anders

….and using the IRig Pre....

Trying to educate myself more…

Here is a good explanation about the difference in sound signal quality when using Balanced mono XLR mic with a soundrecorder/camera having XLR input connections or using adapter cable to the TRS 3.5mm unbalanced input like on a camera.
https://www.youtube.com/watch?v=BMRfmtftGUY

So how to interpret the video to get the best sound quality with ME66/K6 and the LS-11 ?

According to the video you should use XLR cable from the mic to a preamplifier with xlr input and then a short cable from the preamplifier to the TRS 3.5mm unbalanced input on the LS-11. You will gain some 6 dB and get less electrical interference using xlr cable between mic and preamplifier compared to using special adapter cable between mic and the TRS 3.5mm input on the LS-11, an adapter cable like the sennheiser KA 600 Article No. 505633. In this adapter cable xlr pin 2 “hot” goes to both left channel “T” and right channel “R” pin on the TRS and xlr pin 3 “cold” is connected to ground xlr pin 1 (so it is waisted so to speak) which is connected to ground “S” on the TRS. There are no capacitors nor resistors in this cable what I can see and measure. Maybe someone can check the Hosa XVM-105F
cable in this aspect?

Well, a preamplifier like the Beachtech DXA-2T eller Juiced Link Riggy mini series are expensive so using the money to buy a soundrecorder with xlr inputs instead is probably a better way.

So is there a cheaper, small, alternative to use with the LS-11 (or other soundrecorders with 3,5mm TRS input) ?

I found this “hack” of the IRig Pre: http://www.dslrfilmnoob.com/2012/11/25/irig-pre-hack-cheap-xlr-phantom-power-preamp-dslr/

The IRig Pre has an xlr input so it should be designed to use the advantages with balanced mono xlr, I hope….
The Irig Pre is small and powered by a 9V battery, and not that expensive.

If you don’t want to cut & solder, then use an adapter cable for connecting your iphone headset to a pc. I bought such a cable and connected the IRg Pre to it and then took the part of the cable marked with a “microphone” and put it in the LS-11.

It worked, I could increase gain on the Irig Pre, and also, of course, on the LS-11, nice…

So now I wonder how to test if I have got the advantage of the 6dB increase and maybe a bit less sensitivity for electrical interference….hmm….


Please read/look at these too before doing anything you are not sure will work when dealing with balanced/unbalanced electronic audio equipment :

http://www.wildlife-sound.org/equipment/newcomersguide/phantom.html


http://www.megalithia.com/elect/phantech.html
BEWARE: According to this, depending on type of XLR-mic and soundrecorder, you may have to add some capacitors and resistors when using the adapter cable choice, not to damage soundrecorder. So how to find that out one might wonder… better ask before doing anything 

Has anyone tried a balanced to unbalanced microphone transformer with the LS-11, recommendations ?

Thanks,

Anders

The quest for “cheap” and better solutions to connect soundrecorder like LS-11 to ME66/K6 than with the simple adapter cable goes on…..

So what kind of design solutions for balancing are there in the K6 and IRig Pre ?

Here is info about designs: http://www.dpamicrophones.com/en/Mi...de/impedance-balancing-with-active-drive.aspx

1. Signal balancing : Electronic balancing or transformer balancing
2. Impedance balancing


In the specification for the Sennheiser K6 it states that it is “transformerless” so we can rule out transformer balancing here. If you have more info about the design solution, please share!
The K6 has
- Nominal impedans 200 ohm (balanced) and 100 ohm (unbalanced)
- Gain 0dB
- Current consumption 2.2 mA
- Output voltage 2V phantom (6dBV)
- Minimum terminating impedans 1 k ohm


So what kind of designs are there in the IRig Pre?
Here is some of the electronic components I found:

8-pin Chip from TI, M34063A : “1.5-A Peak boost/buck/Inverting switching regulators” (needed to increase supply voltage 9V to 48V to supply the mic with phantom power?)
http://www.ti.com/lit/ds/symlink/mc33063a.pdf

8-pin Chip from TI, R4580i : dual audio operational amplifier (needed to get variable gain), (probably take care of the hot & cold signal from XLR and change it to unbalanced signal ?)
http://www.ti.com/lit/ds/symlink/rc4580.pdf

Some capacitors, resistors, one diode, 2 LED, two small components (inductors) L1 & L2, and a much larger, square & flat, L3 marked with “151”..151mikroHenry? .
A small component where “V1” is written on the board..Vacuum tube ?
One variable resistor

By looking at the component list it looks like it is a “transformerless” solution here too.

For those more savyy than me in electronics, can recombination of the differential signal be done in an acceptable way with impedance balancing with the components in the list?


Hmm…I found this alterative too, BALUN : http://en.wikipedia.org/wiki/Balun
“A balun may also be used instead of an active differential amplifier device.”

For later…when connecting the IRig Pre to the soundrecorder, Olympus LS-11 has at the microphone input: impedance 2 k ohm.

/ Anders

Comparison Beachtek DXA-2T and home made adapter cable

In my ongoing quest to see if I could get better sound using the ME66/K6 with my LS-11, I tested the Beachtek DXA-2T and compared it using my home made adapter cable.

Attached is two recordings of quail at the same place and time with only some few minutes between the recordings.

I had the DXA-2T two volume adjusters turned at the end at unity level so not to reduce input level to the LS-11. I had the LS-11 on max gain.

I tested to put the mic in each of the xlr inputs on the DXA-2T but same results and I changed the switches on it to try to get better results. Best result see attached file.

In this test it seems that the home made cable outperformed the DXA-2T, which I did not expect....

Anders

DXA-2S measurements

I found a Youtube clip from 2009 about the DXA-2S which looks nearly the same as the DXA-2T, same specifications, where the person in the clip tested the frequency response, setting it at 0 dB at 20kHz, and then measuring it getting -15 dB at 20Hz, it should have been within ± 3dB, if I understood it correctly.

https://www.youtube.com/watch?v=hcGNJ1fHo1s

It would be nice to get some measurements on the DXA-2T also....


Anders

Hi Anders,

The trouble is that the DXA-xx is designed as one inexpensive way of getting better sound onto video recordings made on slr cameras with notoriously poor mics and pre-amps, located badly from the point of view of getting a good recording from a good solid sound source in front of the lens. The clips on this link pretty well sell it for this use.

http://www.homebrewaudio.com/pro-audio-for-your-video-review-of-the-beachtek-dxa-2t-camcorder-adapter/

This it does and everyone is so happy that they don't notice some bottom end roll off, or whether you are getting the best performance from the mics, its good enough and no one asks if it should be a lot better.

So it is apparently solving a different problem to yours.

This thread

http://www.videomaker.com/community/forums/topic/dxa-2t-vs-dxa-slr

has someone using an attenuator cable to 'throw away' a number of Db (read the 'Overview' on the Sescom link provided in Bill's response) so that the pro level input matches what the camera can cope with.

Somehow I think that buying a Tascam DR40 as a possible high quality XLR to 3.5mm input for your LS-11 is slightly over the top.

About a year ago I was buying headphone amps and trying to get acceptable performance at minimum cost, the problem was very similar to yours as the quickest way to find out seemed to be was to try them all - not practtical.

You are doing a grand job, however I havn't had access to the type of measuring equipment you are looking for since I graduated from college.

J

Hello Iveljay,

"What you don't know will not hurt you" is an expression that is used sometimes....

I thought I would gain 3dB using balanced XLR to the DXA-2T compared to the simple adapter cable but rather lost some performance instead, at least in the quail comparison.

Yes of course it is best to buy a sound recorder which has XLR-inputs already but the idea with this thread is to see what is possible to do to improve the LS-11 and ME66/K6 combination.

I hope I can get a friend to measure the DXA-2T in the same way as in the video clip.

Anders

Hi Anders,

The reference to the DR40 was that the Bill character wasn't going to use it as a recorder, purely as a balanced XLR to unbalanced 3.5mm adaptor, presumeably through the monitoring channel, hence my comment on over the top. I hope I didn't give the impression that I suggested that you should actually do it.

Anyway taking the route of getting one as a recorder would only exchange one set of problems for others, helicopter noises (from mismatched phantom power ), strange hums and allegedly weak pre-amps to overcome for a starter. Far better to stick to getting the best out of what you have, as you are doing! All these recorders are great as long as you are using them in the way their designer was intending when he created them (not always obvious).

The problem we face is that most audio kit is designed for music or voice and secondly video all of which generally is not running quite so close to the limits as bird recording.

Anyway you have already done a great job clarifying things by your experiments, unfortunately the last time I had access to the sorts of measuring gear needed was when I was a student at University. You don't know any students in need of a project?......

J

I made some not so scientific measurements with the simple adapter cable vs DXA-2T together with the LS-11 and ME66/K6. The sound was generated with my iphone and an app generating sounds with chosen frequency. The sound level was the same between each frequency tested, so was the placement of iphone and ME66/K6. So the results can only be compared at each frequency, not between different frequencies. Gain was at max on LS-11 and nobs on DXA-2T at max, that is unity level. The results are the difference between signals, used Audacity for that, to see spectrum & signal level. The iphone speaker is probably not good at producing 20Hz sounds so I don’t present that here. Based on peak values at frequencies presented by Audacity. I dialled in these on the iphone, 100, 500, 1000, 5000, 10000, 20000 Hz.
Delta = “signal via simple adapter cable in dB” – “signal via DXA-2T in dB”.


Hz / Delta in dB

117 / 5,2
502 / 3,2
996 / 3,6
5017 / 3,9
10013 / 5,2
20007 / 5,5


So the signal via simple adapter cable seems to be the strongest.

Well, I hope my friend can test it with more quality soon.

So I talked to a guy at Lundahl Transformers today about their new product SIB15, which is , as DXA-2T, also a device for going from Balanced XLR to Unbalanced 3.5 mm male plug. It has 1:1 ratio so it should be good.

As he explained, when the signal is generated in the microphone, say 1mV, that signal is divided into a +0.5V signal and a -0.5V signal in opposite phase, and sent out on two separate pins in the XLR-contact and then in the other end, for example in a transformer, the -0.5V signal phase is turned positive again and added to the other +0.5V signal, thus giving a +1mV signal again.
I had got the misconception by looking at explanations on youtube, that there also was an amplification involved, that the +1mV signal was coming also as +1mV signal and an opposite phase signal -1mV to the XLR-contact pins, thus giving an +2mV signal in total in the transformer on the other end….so this is not the case apparently, the balanced XLR-system will only give noise rejection protection, no amplification. Sorry for my slow brain.

So for now, my 2m long simple cable which is shielded, is performing good in my application, no interference while walking near electric cattle fences, seems to outperform the DXA-2T at least in my little test, will be used in the field for now...

I hope my contact can measure the performance of the DXA-2T and maybe the SIB15 too, will see. The SIB15 cost around 2200 SEK incl. VAT.

These kind of devices are probably good to use if having problems with electric interference with your 3.5mm input recorder…but if you are going to buy a recorder, think about getting one with XLR-input right away.
I will stick with my LS-11 for now, it works fine with my ME66/K6 and simple cable.

Anders

Binoseeker said:

As he explained, when the signal is generated in the microphone, say 1mV, that signal is divided into a +0.5V signal and a -0.5V signal in opposite phase, and sent out on two separate pins in the XLR-contact and then in the other end, for example in a transformer, the -0.5V signal phase is turned positive again and added to the other +0.5V signal, thus giving a +1mV signal again.

Click to expand...

The advantage of balanced signal transmission is that at the end you amplify the difference between the two wires. That means that interference picked up by the cable (known as common mode noise) is cancelled.

Resulting signal = Wire1 - Wire2

Wire1 = Signal + N

Wire2 = -Signal + N

Actually a 1 or 2 metre cable shouldn't pick up many interferences unless you are in a very hostile place, the benefits of balanced microphone outputs are better exploited in pro audio when, for instance, you an have a 20 or 30 metre cable run from the stage to the mixing desk.

However, microphones are naturally balanced devices, and especially professional ones. Connecting them to improperly matched unbalanced inputs can be problematic.

That transformer, anyway, is most useful when connecting other kinds of devices, but at that price you can better buy a Marantz PMD661 which already features proper XLR inputs

Borjam, that is a good explanation, thanks!

Anders