Getting Audio right with Virtual Sacrament Meeetings

[joelfinlinson]

I was able to use the Comtek hearing devices in my library with a crab box and two cables. A 3.5 mono cable on each end that goes from the Comtek to the crab box and then a 3.5 stereo cable on each end that goes from the crab box to the 3.5 mic input on a laptop. The sound is great if the Comtek is turned to position 3 of 12 on the adjustment.

Here are the parts from Newegg if you're interested:



StarTech.com MU3MMSRA Slim 3.5mm to Right Angle Stereo Audio Cable Male to Male

StarTech.com MU3MMSRA Slim 3.5mm to Right Angle Stereo Audio Cable
Item #:N82E16882203140
Return Policy: 45/1 Return Policy

$4.95

Add StarTech.com MU3MMSRA Slim 3.5mm to Right Angle Stereo Audio Cable to cart
1
SYBA SD-CM-UAUD USB 2.0 External Stereo Audio Adapter

SYBA SD-CM-UAUD USB 2.0 External Stereo Audio Adapter
Item #:N82E16812186035
Return Policy: 45/1 Return Policy

$9.29

Add SYBA SD-CM-UAUD USB 2.0 External Stereo Audio Adapter to cart
1
Steren ST-255-155 2 ft. 3.5 Mono Plug to 3.5 Mono Plug Cable

Steren ST-255-155 2 ft. 3.5 Mono Plug to 3.5 Mono Plug Cable
Item #:9SIA00Y8965463
Sold by UnbeatableSale

[BrandonBates]

FYI after some research I built a "simple" DC isolating pi attenuating pad to let an assisted listening device see a 32 ohm load and a phone see a 2k microphone (to trigger the phone to see a microphone) with a 40db attenuation to turn line to mic. Using one of the newer "listen" devices at 100% feeding into iphone hits good levels (with some headroom). In theory it should work with the comtek devices that look for a headphone load to turn on/stay on. Haven't tried with android. Used some components I had around except the jack cables, which I got pre-cut & stripped ones from amazon. I heatshrinked it together to make a solid cable. Components: TRRS cable, TRS cable, 32 ohm resistance (used 22+10 in series), 10k resistor, 10uF capacitor (to block iphone mic power or any dc on the listening device output), then 2k resistor. 32 ohm across TRS tip and sleeve, tip signal series through 10k, then positive of capacitor to 10k, negative of cap to last ring of trrs, 2k load across last two rings, 2nd to last ring of trrs and sleeve of first (ground signal) tied together. Going to still make a few more cables but I've got 50' headphone extension cables to connect to the recorder out line level, but I'll use this adapter. Assisted listening devices were just too noisy (might try to find a better tuner, wireless is nice, it's just 72.1MHz)

[russellhltn]

FYI after some research I built a "simple" DC isolating pi attenuating pad to let an assisted listening device see a 32 ohm load and a phone see a 2k microphone (to trigger the phone to see a microphone) with a 40db attenuation to turn line to mic. ... Going to still make a few more cables but I've got 50' headphone extension cables to connect to the recorder out line level, but I'll use this adapter. Assisted listening devices were just too noisy (might try to find a better tuner, wireless is nice, it's just 72.1MHz)

32 ohms is fine for the receivers, but may be a bit low for the record out. I'm not sure of the exact specss, but it's being driven by a 600 ohm line level system though a transformer. I think the transformer is more isolation then step up or down. And it's fewer parts. I just used a 120K and 1.2K resistors in a L pad arrangement.

[CalS201]

When building your own attentuator that connects the chapel "Record Out" jack to the iPhone, IPad, or most laptops using a TRRS connector, the following info should prove helpful.

It should be noted that you can buy a similar attentuator, https://www.amazon.com/Headset-Buddy-Li ... B078HGFS3Z, on Amazon.

Code: Select all

          RECORD                   DIY                     IPHONE/IPAD
          OUT JACK             ATTENTUATOR                   (V+)
                                                               | 
                                                             (?? K)
[V1]                  [V2]   [C1]      [R2]  [V3]              |
300mv-)|(---< [T]RS <------(-10uf+)---(22K)------> TRR[S] >---[V4]
      )|(              |                      |   
  600 )|(            (22K) [R1]         [R3](2.2K)
  ohm )|(              |                      |
 -----)|(---< TR[S] <----------------------------> TR[R]S >---

V4 = 30mv rms. It is the maximum allowed audio input to the iphone/ipad. Distortion will occur above 35mv. A DC bias is also present. If you plug in anything with 1-3K resistance the DC bias drops to 1-2V, which will activate the microphone input circuit.

V3 is the output level of the attentutor and should be at least 15mv, but less than V4(30mv)

V1 is about 300mv rms at the record out jack when someone speaks loudly into pulpit mic.

V2 is the same as V1 when attached attentuator load impedance is greater than 10 X 600ohms (best practice). The load impedance should always be the same or greater than the 600 ohms source impedance of the record out transformer.

R1 & C1 are optional. C1 is good practice to isolate a transformer from any DC bias in the circuit. It can often be eliminated when the DC bias is small (like from the iPhone).

For the circuit values shown, the iphone will receive about 26mv, which is ideal.

FORMULAS
If V1 = 300mv then
V2 = V1 * R1/(600+R1) = 292mv
V3 = V2 * R3/(R2+R3) = 26.5mv

The impedance seen by RecordOut transformer is about 11K.
The impedance seen by the iPhone is about 2K

[drepouille]

I ordered a 50-foot 3.5 mm stereo cable to see if I can use the Record Out jack under the Sacrament table. I've discovered that most modern desktop and laptop computers can accept either mic-level input or line-level input without using an attenuator.
So I have several audio options:

• Record Out jack with 50-foot cord
• Webcam mic
• Wired Lavalier mic with 16-foot cord, taped to the mic boom on the podium
• Wireless Lavalier mic, taped to the mic boom on the podium
• Comtek ALS receiver

With three wireless options and one really long cord, I can probably move the camera and computer off to the side of the room, where it is out of the way, and not so obvious.

[russellhltn]

Code: Select all

          RECORD                   DIY                     IPHONE/IPAD
          OUT JACK             ATTENTUATOR                   (V+)
                                                               | 
                                                             (?? K)
[V1]                  [V2]   [C1]      [R2]  [V3]              |
300mv-)|(---< [T]RS <------(-10uf+)---(22K)------> TRR[S] >---[V4]
      )|(              |                      |   
  600 )|(            (22K) [R1]         [R3](2.2K)
  ohm )|(              |                      |
 -----)|(---< TR[S] <----------------------------> TR[R]S >---

Nice ASCII art. I'm stealing that to illustrate my DIY cable as soon as I check some things.

Some comments: R1 isn't needed except to give a lower load to the source. But most sources don't care if they see a higher impedance.

I left out C1 as the amount of DC current is too small to be a concern, especially knowing that the output is a transformer. I might leave both in if the source were an amplifier output. But 2V though a 22K resistor is 0.091 mA, or 91 micro-amp. It doesn't seem like much of a concern.

One thing I'm puzzling over is everyone seems to be using a 20dB attenuation while I found I had to use 50dB to avoid distortion or clicking on my Android.

[drepouille]

I bought a 50-foot 3.5 mm audio cable, and used it to connect the Record Out jack under the Sacrament table to the "line level" input jack on a Dell Optiplex desktop. The signal was not strong enough. So I moved the cable from the "line level" input jack to the microphone input jack on the desktop. It worked perfectly!

I checked the Microphone Properties Levels settings. The microphone was set to 100%, and the microphone boost was set to +20.0 dB.

I wanted to try this way back in July when I began broadcasting Sacrament meeting, but I was scared that the "line level" signal would blow out my microphone jack. It didn't.

[russellhltn]

The signal was not strong enough. So I moved the cable from the "line level" input jack to the microphone input jack on the desktop. It worked perfectly!

Does the front of the "record out" jack say "Microphone level"? There is a version that can be ordered from EMTech, but I've not seen it installed in a church building before.

I wanted to try this way back in July when I began broadcasting Sacrament meeting, but I was scared that the "line level" signal would blow out my microphone jack. It didn't.

Line level into consumer "mic in" will not physically damage anything. But it will "blow out" the sound.

[CalS201]

russellhltn wrote:
One thing I'm puzzling over is everyone seems to be using a 20dB attenuation while I found I had to use 50dB to avoid distortion or clicking on my Android.

The iPhone/iPad devices have a maximum microphone level of about 30mv so a 20db pad (divide by 10) correctly reduces the 300mv signal from the record out jack.

I believe Android phones have a maximum microphone level of 12mv for some models.
http://www.technical-direct.com/en/smar ... -audio-ii/
This requires a 26-30db pad to avoid distortion. Your 40-50db pad would drop the 300mv RecordOut signal down to 1-3mv which is extrememly low. Maybe your chapel's RecordOut jack is outputting a level higher than 300mv.
http://www.technical-direct.com/en/smar ... -audio-ii/

[russellhltn]

The iPhone/iPad devices have a maximum microphone level of about 30mv so a 20db pad (divide by 10) correctly reduces the 300mv signal from the record out jack.

Nit-pick, 0VU for consumer line-out is −10 dBV, or 0.316Vrms, 0.447Vpeak. Not 0.300V.

But if the iPhone distorts at 35, that's not leaving you any overhead for peaks. (difference between VU and peak reading meters/peak light) I'd think you'd want at least an additional 10dB so to have some headroom. Especially since we don't know if there's any compressors or limiters in the chain.

While we want a good solid signal, what we really need is something our apps can work with comfortably without having to turn up the gain to the point we start noticing the noise floor.

I'd be curious to hear how your cable works with a known consumer line-out signal, such as from a home stereo.