microphones with conventional TRS connectors
It is rather rare here in the 21st century to find microphones with 1/4 inch phone connectors, either TS or TRS. Virtually all microphones in modern times are using either "professional" XLR connections, or "amateur" 3.5mm (as for portable gear like consumer camcorders, voice recorders, etc.)
If you could clarify what you are doing with this and what kind of microphones you want to accommodate, it would be easier to answer your question.
powered XLR inputs.
"Pro" XLR mic inputs are often provided with the (switchable) option of Phantom Power. This started out as 48V (for historic reasons), but most modern microphones which require phantom power will operate on lower voltages like 24V or even 12V.
Can anybody clarify which are the conventional nominal levels used between the two connectors and types.
XLR connectors are commonly used for both line-level and mic-level signals. In many cases the level of the XLR input (or output) is user-selectable for mic-level or line-level. In very rough, back-of-the envelope terms, you can think of line-level as 1V, and mic-level as 1mV. That is why typical mic preamp circuits have around 60dB of gain. (1000x)
1/4 inch connectors are used primarily for four different kinds/levels of audio signals:
- Line-level. Same signals as used with XLR. Generally XLR and TRS line-level connections are equivalent and interchangeable. Of course TRS allow for a balanced signal interface while TS connectors support only unbalanced.
- Instrument-level. This is the signal that comes out of an electric guitar (or bass, etc.) Traditionally quite high-impedance (~100K vs. 1K-10K for line-level) and quite low signal-level (equivalent to mic-level)
- Headphones. In modern times TRS, but stereo, unbalanced with common/ground on Sleeve, and Left channel on Tip, and Right channel on Ring. Signal levels roughly equivalent to line-level and quite low impedances 20-150 ohms
- Effects Insert. Used in mixers as an "interrupt" to the normal path. So that the channel signal can be pulled out an sent through an external process (limiting, compression, reverb, etc.) and then back into the channel. A "closed-circuit" TRS jack is used where the Send (Ring) is connected across to the Return (Tip) wen nothing is plugged in. Signal levels are typically at (or slightly lower than) line-level.
Also for metering on a mixing console, do the conventional slider controls with the 'chasing' LEDs measure a rectified average, peak or VU because again,
While there are some (rare) examples where LED arrays show the "setting" of a slider control, they are typically used to meter the audio levels regardless of whether slider controls are used or not. I will assume you are asking about audio level monitoring and not control position(?)
I can't really get a clear answer. I've had many 'dunnos' but to me there's quite separate concepts!
Perhaps because there are many ways of doing that depending on the application, the budget (cost of the gear), etc. For critical, professional (broadcasting, studio recording/mixing) applications LED meters frequently have special "ballistics" and calibration. And even at that, there are different standards in America vs. European practice. So it somewhat depends of where you are as well.
If you are just doing a small hobby project, simply start with something simple like a fast-responding "peak" reading meter circuit. When you start playing with it you will see the advantages and disadvantages of peak-reading vs. averaging (RMS, traditional "VU") metering of audio signals. Don't sweat it. Start with something simple and improve/enhance your circuits as you gain experience with design, construction and (most importantly) actually using the gear.
A very popular (and easy) solution for LED-string audio metering are the TI chips LM3915 and LM3916. I very strongly suggest downloading the data sheets for these chips. They enable you to construct a quite decent meter with the single chip, a string of LEDs, and a few resistors and capacitors.
Also, the LM3915/16 data sheet and application notes show audio signal processing circuits that implement: Half-Wave Peak detector (Fig. 17), Precision Half-wave Rectifier (Fig. 18), Precision Full-Wave Average Detector (Fig. 19) and Precision-wave Peak Detector (Fig.20)
Many pieces of commercial audio gear use these chips (or equivalent) to implement LED-ladder style audio-level metering.
Note that there are hundreds of reference designs out there on the internet for mic-level and line-level input and output circuits. Of particular interest are the products made by THAT Semiconductor and many specialized audio chips made by TI and Analog Devices. There are also schematic diagrams for many popular audio mixers available for study (or home construction).
LM3915/16:
https://media.digikey.com/pdf/Data%20Sheets/Texas%20Instruments%20PDFs/LM3814,15.pdfTHAT Semiconductor:
http://www.thatcorp.com/THAT_IC_Products.shtmlTI Audio ICs:
http://www.ti.com/audio-ic/overview.html?keyMatch=audio&tisearch=Search-EN-EverythingAnalog Devices ICs:
http://www.analog.com/en/applications/markets/consumer-pavilion-home/proav.html