If I follow with LM386 stage, what is the advantage of using the ne5532 at all?
I ask this earnestly as I am wondering when the ne5532 would/should be used...
The LM386 is designed for a line-level signal input. So you need some amount of additional voltage gain if your source is a low-level source like a microphone. The NE5532 is designed for amplifying low-level signals (microphone, phonograph pickup, electric guitar, etc.) up to line-level. And with better signal-to-noise ratio than common general-purpose monolithic op-amps.
Also is the term "line level" considered a norm for small signal transfer between devices?
Yes most audio gear uses "line-level" internally. And also "line-level" externally to connect between different pieces of gear.
There are roughly three levels of audio signal standards:
1.
Low-level - this includes mic-level, phono-level, instrument-level, etc. Typically down at a few millivolts. Modern microphones are low-impedance sources (a few hundred ohms), Phono-level are typically 47K ohm impedance, and electric instruments (guitar, bass, etc.) expect to see no lower than 100K load impedance (or higher)
2.
Line-level - There are two varieties of this, Consumer line-level is typically -10dBv (somewhere around 300mV), and Professional line-level (+4dBv to +10dBv) which is typically around 1.2V Modern gear has rather low output impedance (perhaps a few hundred ohms to maybe 1K ohm source impedance. And modern gear typically has rather high input impedance (perhaps 5K to 10K or 20K ohms. That convention generally eliminates cable effects (parallel capacitance and series resistance) from consideration, and makes "impedance matching" something that only our grandfathers remember.
3.
Speaker-level - Typically a very low source-impedance from a power amplifier designed to drive a 8 ohms (or 4 or 16 ohms) load from a passive speaker cabinet. Voltage depends on the amplifier power. Around 9V for 10 Watts into 8 ohms, or 28V for a 100 Watts into 8 ohms. Ohm's law will translate watts into volts for a given impedance (
http://rcrowley.com/eirp.htm)
(I take it that LINE LEVEL means kohms and very small millivolts, but I could be wrong about that also)
No. Line-level does not mean K ohms of impedance, and certainly does not mean small mV of signal level. See outline above.
As @Hero999 observed, you are trying to use an electret microphone capsule. Electret microphones do not generate any signal on their own (as a dynamic microphone would). They actually have a FET transistor inside with "sound" connected to the gate. So you must put some current through it in order to get a voltage signal out of it. There are hundreds of representative circuits on the interweb showing electret condenser microphone circuits connected to the input of an NE5532.