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match digital audio recorder input singal strength spec with 16.4.2 Aux output signal strength spec
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alanchu
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Joined: 16/02/2014 23:40:56
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Hello,

My church is using a Presonus 16.4.2 connected to a PC for sound mixing and worship/sermon recording. The PC is running Window 8. We are having intermittent problem with the Capture 2 program. During the middle of a recording session, from time to time the Capture 2 program would stop recording. This would happen once per Sunday and the time of occurrence is random. The other program that is running at the same time during the recording is the VSL.

Last Sunday just right before Capture 2 stopped recording, I was looking at the spectrum analyzer (waterfall) on the VSL, and I notice the waterfall stopped scrolling for about 1 second, and then after that I saw Capture 2 stopped recording, and the VSL spectrum analyzer started to work again (waterfall started to scroll) It is probably a firewire issue. We have given up on solving this problem.

We are thinking about buying a digital audio recorder. I know that the Aux output, the Tape output, and the CR output are all rated at 18 dBu maximum. 18 dBu is about 6.16 V if I do my math correctly. I am just trying to make sure that the output from our mixer is not going to be too hot for the input spec of a digital recorder. If you guys have any thoughts or have spotted an error on my part, please let me know.

One of the digital recorders (Zoom H4n) we are considering have a input power spec ranged from -10 dBm to -42 dBm for balanced input and from +2 dBm to -32 dBm for the unbalance input. The input impedance is 1000 ohm for balanced input and 480000 ohm for unbalanced input. Translate this to input voltage in base 10 number, for balanced the input voltage ranges from about 0.32 V to 0.008 V. For unbalanced, the input voltage ranges from 27.6 V to 0.55 V. It looks like we can use the Tape Output (RCA unbalanced) to send signal to this digital recorder. (RCA to unbalanced TRS). This recorder also has a 1/8" phone jack, but I don't have the spec value to determine the input signal range.

The other digital record is the Tascam DR-05. Its nominal input signal strength is -20 dBV and the maximum input signal strength is -4 dBV. The input impedance is 25000 ohm. Translate the input signal values to base 10 number, the nominal input is 0.1 V and 0.63 V for the maximum. It looks like our mixer output may be too hot for this device.

Please let me know if you see any error on my part or issues I need to consider.
Thanks in advance.

Alan
alanchu
Prenoob

Joined: 16/02/2014 23:40:56
Messages: 7
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Hello,

We tested the setup today using the Tape Out from the mixer with the H4N using the unbalanced input. When the worship team was singing (one notch into the yellow the main on the mixer), the signal strength indicator on the recorder is about -12 dB. During the sermon with the signal output from the mixer going from -10 dB to maybe -5 dB, the signal strength on the recorder was below -24 dB. I tried to use the two track out dial to improve the signal strength, but it doesn't seem to do anything.

We also ordered two audio attenuators. One of them is a selectable with a maximum attenuation of 25 dB. The other one is a straight 50 dB to bring a line voltage down to the 3.5mm mic input level. I expect the second attenuator to arrive before next Sunday. Will report back with our results.

One of the difficulties in this exercise is that different product uses different unit in their spec. The mixer uses dBu, one of the recorder uses dBV and impedance, and the third one uses dBm and impedance. The other difficulties I had was to convince the other people in the team that the voltage range don't match with these three equipment. Since one of the recorder had a XLR/TRS connector, people (including me) assumed it would be compatible with our mixer. Needless to say I was really surprised.


roblof
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Joined: 12/04/2011 21:33:08
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Most devices using xlr/trs combo connectors are using different levels.

The xlr's are usually mic levels and the trs line levels. Are you using a trs cable to connect to your recorder?

Also, some recorders can change its input sensitivity in their menu. Some even have builtin pads

You should normally not need any attenuators, at least not on the few recorders that i've seen. Try the tape outputs (the rca connectors) on the studiolive. They have much lower output than the other outputs.
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SwitchBack
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Joined: 17/02/2011 01:10:03
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alanchu wrote:Hello,

We tested the setup today using the Tape Out from the mixer with the H4N using the unbalanced input. When the worship team was singing (one notch into the yellow the main on the mixer), the signal strength indicator on the recorder is about -12 dB. During the sermon with the signal output from the mixer going from -10 dB to maybe -5 dB, the signal strength on the recorder was below -24 dB. I tried to use the two track out dial to improve the signal strength, but it doesn't seem to do anything.

We also ordered two audio attenuators. One of them is a selectable with a maximum attenuation of 25 dB. The other one is a straight 50 dB to bring a line voltage down to the 3.5mm mic input level. I expect the second attenuator to arrive before next Sunday. Will report back with our results.

One of the difficulties in this exercise is that different product uses different unit in their spec. The mixer uses dBu, one of the recorder uses dBV and impedance, and the third one uses dBm and impedance. The other difficulties I had was to convince the other people in the team that the voltage range don't match with these three equipment. Since one of the recorder had a XLR/TRS connector, people (including me) assumed it would be compatible with our mixer. Needless to say I was really surprised.

Hi,
I can see how the different ways of specifying output levels and input sensitivities can be confusing, but frankly I wouldn't worry about it too much. Only two things to keep an eye on here:
- Connecting a line output to a mic input requires attenuation. 20-40dB attenuation will get you in range.
- High impedance outputs can't drive low impedance inputs. Transformation is needed to bring output impedance well below input impedance.
DI-boxes perform both those functions. A stereo DI-box is the best choice for your application.

As for the choice of mixer outputs for recording I would avoid outputs that have their output levels controlled by the main out fader (like tape out) or you'll always struggle with the compromise between FOH and recording level. Better to reserve a pair of auxes for the recording. That will give you much more control over the recording level and in fact the whole recording mix. E.g. it allows you to add more to the recording mix from those instruments missing from the FOH mix because they don't need room amplification. Added bonus on the SL mixers is the compressors you can use on the 'recording auxes' outputs. Using them can greatly reduce the risk of clipping the recorder inputs.

Oh, and a thing to try regarding the 'once per sermon' Capture stop: After booting the system before the sermon (connect everything, start the mixer, wait a little, boot the computer, wait until fully booted) restart the computer! (so don't shut down completely). See if that prevents the Capture hickup. It does with a Windows laptop I use. Don't ask me why, it simply does...

This message was edited 1 time. Last update was at 09/06/2014 15:52:10

alanchu
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Joined: 16/02/2014 23:40:56
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roblof wrote:Most devices using xlr/trs combo connectors are using different levels.

The xlr's are usually mic levels and the trs line levels. Are you using a trs cable to connect to your recorder?

Also, some recorders can change its input sensitivity in their menu. Some even have builtin pads

You should normally not need any attenuators, at least not on the few recorders that i've seen. Try the tape outputs (the rca connectors) on the studiolive. They have much lower output than the other outputs.


Roblof,
Thank you for your comments and suggestions.

The connection from the mixer to the H4N recorder is as followed:

Mixer Tape Out ->RCA

RCA cable has RCA on one end and a 3.5mm (don't know if is is a TRS or not) on the other end. The 3.5 mm is connected to a 3.5mm to 1/4 TRS adopter
H4N input <-1/4 TRS

I found out that the H4N allows one to set input sensitivity. Because initially I was not sure if the H4N has enough intelligence to figure out the incoming signal is balanced or unbalanced, so I had the sensitivity set to minimum.

The 16.4.2 Tape Out is rated 18dBu, just like the Aux Out, but the impedance for Tape Out is 100 ohm instead of 51ohm like Aux Out. Does this mean less power coming out of the Tape Out? (P = V^2/Z)

Thanks again,
Alan
alanchu
Prenoob

Joined: 16/02/2014 23:40:56
Messages: 7
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SwitchBack wrote:
alanchu wrote:Hello,

We tested the setup today using the Tape Out from the mixer with the H4N using the unbalanced input. When the worship team was singing (one notch into the yellow the main on the mixer), the signal strength indicator on the recorder is about -12 dB. During the sermon with the signal output from the mixer going from -10 dB to maybe -5 dB, the signal strength on the recorder was below -24 dB. I tried to use the two track out dial to improve the signal strength, but it doesn't seem to do anything.

We also ordered two audio attenuators. One of them is a selectable with a maximum attenuation of 25 dB. The other one is a straight 50 dB to bring a line voltage down to the 3.5mm mic input level. I expect the second attenuator to arrive before next Sunday. Will report back with our results.

One of the difficulties in this exercise is that different product uses different unit in their spec. The mixer uses dBu, one of the recorder uses dBV and impedance, and the third one uses dBm and impedance. The other difficulties I had was to convince the other people in the team that the voltage range don't match with these three equipment. Since one of the recorder had a XLR/TRS connector, people (including me) assumed it would be compatible with our mixer. Needless to say I was really surprised.

Hi,
I can see how the different ways of specifying output levels and input sensitivities can be confusing, but frankly I wouldn't worry about it too much. Only two things to keep an eye on here:
- Connecting a line output to a mic input requires attenuation. 20-40dB attenuation will get you in range.
- High impedance outputs can't drive low impedance inputs. Transformation is needed to bring output impedance well below input impedance.
DI-boxes perform both those functions. A stereo DI-box is the best choice for your application.

As for the choice of mixer outputs for recording I would avoid outputs that have their output levels controlled by the main out fader (like tape out) or you'll always struggle with the compromise between FOH and recording level. Better to reserve a pair of auxes for the recording. That will give you much more control over the recording level and in fact the whole recording mix. E.g. it allows you to add more to the recording mix from those instruments missing from the FOH mix because they don't need room amplification. Added bonus on the SL mixers is the compressors you can use on the 'recording auxes' outputs. Using them can greatly reduce the risk of clipping the recorder inputs.

Oh, and a thing to try regarding the 'once per sermon' Capture stop: After booting the system before the sermon (connect everything, start the mixer, wait a little, boot the computer, wait until fully booted) restart the computer! (so don't shut down completely). See if that prevents the Capture hickup. It does with a Windows laptop I use. Don't ask me why, it simply does...


Thank you Switchback,

Very good point on the use of Aux and the compressor. This means the Aux output has three ways of making sure the dynamic range will fit into the recorder.

I think you are right about the computer reboot thing. Now I come to think of it, In the past when we reboot the computer, the recording operation tends to run smoother.

Thanks again for your comments and suggestion.

Ala

alanchu
Prenoob

Joined: 16/02/2014 23:40:56
Messages: 7
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This Sunday we used the Tascam DR-05 digital recorder (a gift from one of the brothers). We routed signal from Aux out with a variable attenuator between the Aux out and the DR-05. Since the DR-05 uses the mic (3.5 mm) input, we had to use an adopter (TRS to 3.5 mm). Initially I had the attenuator set to 20 dB during practice with the Aux out output dial set at 2 o'clock position, but later on I changed the attenuation to 15 dB with the Aux out dial set to 10 o'clock position. The reason for this is to bring the input signal strength closer to the nominal operating point with out turning the dial all the way to the right. The setting for the individual channel input contribution to the Aux was nearly max out.

I will find out later on this week from a brother who is in charge of post processing audio recording whether the signal strength is stronger than last week's recording. He told me this morning that signal strength from last week's recording was weak, and he had to boost it. I told him that I was expecting it to be weak. The difference in the maximum signal magnitude format is about 13 dB, i.e 20*log (27/6) = 13 dB, and since sermon was running at 10 dB below the u on the main channel, so all together the sermon was 23 dB down. So far everything is meeting my expectation and calculation results.

The lessons I learned from this experience is that it pays to read the specification so I can anticipate potential problems before hand. I still need to find a better way to communicate the results with the rest of the team. It just seems that the rest of the team form their ideas/belief based on their prior experience, and when I bring them my analysis results based on specification, they don't know what to do with it.

Thank you all for your patience and suggestions.
Al





 
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