I recently purchased one of these little gadgets, a handheld solid state recorder with 32G memory and rechargeable battery.
It wasn't expensive and is surprisingly solidly build and heavy for its size. It records various flavors of MP3 and Wav formats. I got it to use with some little mics I made, some of which are worn like earbuds. It was meant to be a very light and easy thing to carry for field recordings and such. But it failed to work - maybe.
When I did test recordings, I found that using the internal mic, only the left mic is recorded, nothing from the right. The left mic is recorded on both tracks, nothing comes from the right. So I tried with the external mics plugged in. Nothing but the left mic recorded, but this time the left mic wasn't routed to both channels. Then I tested Line In (there is a software switch) and got perfect stereo flat from 20Hz to 22kHz both channels working as they should. The left channel recorded on the the left track, the right channel recorded perfectly on the right track. Hmmmmm......
Since the PUI mic capsules I have put out a whopping good level (too much for the mic input) I tried the Line In setting with the mics plugged in. It works! But again, no signal on the right. Even though from the computer line level signal the right side recorded perfectly. If Line In works on both channels with an input from a line source, why does using the same setting with mics result in recording only the left channel? This had me puzzled, so I had to drink some rum and think about it.
Some of you will have already guessed the problem.
It occurred to me that the problem had to be the mic power. To power the mic capsules "Plug-in-Power" uses a 3V bias on the line. Maybe the right side has no 3V. An input from a computer or other line source doesn't need the 3V to function, but the mics do. What if only the tip of the 3.5mm plug had the 3V bias, and the ring didn't? Sure enough, that's the case. 3V on the tip, nothing on the ring. That's both in Mic and Line settings. That means that if I can get 3V to the right side (ring) of the connector, the right external mic will work. But how? I'm not even sure I can get the thing apart. Then I have to figure out how not to get crosstalk thru the 3V supply.
Any ideas?
When I did test recordings, I found that using the internal mic, only the left mic is recorded, nothing from the right. The left mic is recorded on both tracks, nothing comes from the right. So I tried with the external mics plugged in. Nothing but the left mic recorded, but this time the left mic wasn't routed to both channels. Then I tested Line In (there is a software switch) and got perfect stereo flat from 20Hz to 22kHz both channels working as they should. The left channel recorded on the the left track, the right channel recorded perfectly on the right track. Hmmmmm......
Since the PUI mic capsules I have put out a whopping good level (too much for the mic input) I tried the Line In setting with the mics plugged in. It works! But again, no signal on the right. Even though from the computer line level signal the right side recorded perfectly. If Line In works on both channels with an input from a line source, why does using the same setting with mics result in recording only the left channel? This had me puzzled, so I had to drink some rum and think about it.
Some of you will have already guessed the problem.It occurred to me that the problem had to be the mic power. To power the mic capsules "Plug-in-Power" uses a 3V bias on the line. Maybe the right side has no 3V. An input from a computer or other line source doesn't need the 3V to function, but the mics do. What if only the tip of the 3.5mm plug had the 3V bias, and the ring didn't? Sure enough, that's the case. 3V on the tip, nothing on the ring. That's both in Mic and Line settings. That means that if I can get 3V to the right side (ring) of the connector, the right external mic will work. But how? I'm not even sure I can get the thing apart. Then I have to figure out how not to get crosstalk thru the 3V supply.
Any ideas?
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I guess if you can get at the battery inside? Unsure if the device has it's own battery like a cell phone, or replaceable AA batteries? That's just soldering a wire to a battery terminal is a lot easier than to some micro-sized component on its main board - after getting it all apart.
You're several steps ahead of me, as I want to do the exact same thing, only I bought an old Tascam DR05. I dont have mics yet and dont know where to get them. I did experiment with in-ear mics and successfully tricked my wife into thinking the speakers were playing, when she had "open" headphones on. Playing a recording of my speakers playing that I made with the in-ear mics.
I'd like to be able to present and here's how it sounds via a link to an audio file, as others do - but a little bit better than just a stupid cell phone recording. When I look at my Sony cyber-shot, it's got two little oval holes about 3/4" apart with the word "STEREO" printed in between. One would think such a manufacturer would consider some customers would care to do "a little bit better" than that, but no external mic option is provided. So much for video.
I realize it'll never be perfect with all the variation in headphones and only works with headphones, but still - so much closer. I'll be keeping in touch with this thread, for sure.
You're several steps ahead of me, as I want to do the exact same thing, only I bought an old Tascam DR05. I dont have mics yet and dont know where to get them. I did experiment with in-ear mics and successfully tricked my wife into thinking the speakers were playing, when she had "open" headphones on. Playing a recording of my speakers playing that I made with the in-ear mics.
I'd like to be able to present and here's how it sounds via a link to an audio file, as others do - but a little bit better than just a stupid cell phone recording. When I look at my Sony cyber-shot, it's got two little oval holes about 3/4" apart with the word "STEREO" printed in between. One would think such a manufacturer would consider some customers would care to do "a little bit better" than that, but no external mic option is provided. So much for video.
I realize it'll never be perfect with all the variation in headphones and only works with headphones, but still - so much closer. I'll be keeping in touch with this thread, for sure.
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The recorder has a built in rechargeable battery. But I haven't found a way to get inside it yet.
I did three rounds of tests, and in the first round any mic recording was only the left mic - and it want to both tracks of the recording. No good, I need left and right separate.
On round two, I saw the left external mic recorded to the left channel, nothing on the right channel - they were not combined. That gave me hope.
But on round three today, I see the left external mic on both recorded tracks again. 🙁 Did I imagine round two?
I can understand why they would build the mic input with bias power only on the tip, as that would be what a typical mono external mic would use. There might be no ring connector at all.
But of course the thing shouldn't have a bias voltage on Line In setting anyway. So much for logic.
Before I bought this I was using the Zoom H4n which does have a 3.5mm stereo mic input with proper bias for both channels. It does a great job, but I was hoping for something much smaller and not as battery hungry. The Zoom goes thru AA batteries mighty quick. I had to buy rechargeable AAs
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I did three rounds of tests, and in the first round any mic recording was only the left mic - and it want to both tracks of the recording. No good, I need left and right separate.
On round two, I saw the left external mic recorded to the left channel, nothing on the right channel - they were not combined. That gave me hope.
But on round three today, I see the left external mic on both recorded tracks again. 🙁 Did I imagine round two?
I can understand why they would build the mic input with bias power only on the tip, as that would be what a typical mono external mic would use. There might be no ring connector at all.
But of course the thing shouldn't have a bias voltage on Line In setting anyway. So much for logic.
Before I bought this I was using the Zoom H4n which does have a 3.5mm stereo mic input with proper bias for both channels. It does a great job, but I was hoping for something much smaller and not as battery hungry. The Zoom goes thru AA batteries mighty quick. I had to buy rechargeable AAs
What do you want? Maybe I can help. It's easy to make your own.
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It's not too hard to make an adapter for mic inputs that don't provide plug-in power. 3V (or so) battery, 2.2K pull-up resistor, 4.7u capacitor to block the DC.
Three ideas, all inelegant and inconvenient:
External microphone supply, but that means carrying around an extra box with a battery, resistors and coupling capacitors.
Putting a resistor of 2.2 kohm or so between the left and right microphone inputs, so both mikes get sort of supplied. You get lots of crosstalk, but as long as it is predictable, you can correct for it afterwards. Channel separation after correction will still be poor.
Gyrator-like simulated inductor circuit between tip and ring, designed to suppress crosstalk while conducting DC. Where to find space for it?
External microphone supply, but that means carrying around an extra box with a battery, resistors and coupling capacitors.
Putting a resistor of 2.2 kohm or so between the left and right microphone inputs, so both mikes get sort of supplied. You get lots of crosstalk, but as long as it is predictable, you can correct for it afterwards. Channel separation after correction will still be poor.
Gyrator-like simulated inductor circuit between tip and ring, designed to suppress crosstalk while conducting DC. Where to find space for it?
Thanks! I'm trying to get the PUI AOM-5024L-HD-R electret capsules. Harder is to design a clip, or a bud, or a foam insert to hold a capsule just at the outside of the ear canal. Then get the wires to something as a strain relief, so the weight of a connecting cable doesnt just yank the mics out of position. I know Bose has a neck band design for some of their noise cancelling earphones.
I found this within the actual ear lobe itself mounting necessary for the "is it the headphones or speakers?" playback illusion to work.
Started with the Bose Adaptiq mics, like this one https://www.ebay.com/itm/175182117456, finding their headband based, near-ear mounting close, but no cigar. I then pulled the capsules from that, which worked pretty good mounted to a set of foam ear plugs. Those eventually got ruined trying to mount and retrieve them to and from a foam fashion display head, which was also close, but no cigar.
FWIW I got my Tascam DR-05 yesterday. Verified operation on installing batteries, for playback at least. Even came with a 4G card that someone didnt bother to erase, as it contained a couple short but cute "girl with guitar" recordings...and a 1:20:00 long one-sided recording of her talking to some guy on the phone.
The device does do stereo, for sure. But only on the Line In setting. I "thought" that it had once recorded in stereo with the Mic setting, but either it was a glitch or I was mistaken. The firmeware must switch to mono for anything but the line level setting. Too bad.
If it won't do stereo with the gain set for mics, it really won't do what I need. I could build a little SMD mic preamp with a THAT or MAX SMD chip and go in line level - but it would be at best a clumsy lump that has to tag along. That defeats the advantages of such a small, light unit. I can pop this in my pocket and forget that it's there.
Some good ideas in your posts, thanks.
I had thought about a few, some were novel thinking. 🙂 I fear than anything done outboard would either be too big to be practical or cause too much crosstalk.
The seller has refunded my purchase and told me to keep the recorder. Too bad, as it's a clever little unit, has long battery life and is super easy to use. The Sony ICD-PX470 is the logical step. But it's $18 more, is larger, has a lot less memory and doesn't have a rechargeable battery. But it does do stereo on the mic input according to one Amazon reviewer who tested it with a Sony stereo mic.
If it won't do stereo with the gain set for mics, it really won't do what I need. I could build a little SMD mic preamp with a THAT or MAX SMD chip and go in line level - but it would be at best a clumsy lump that has to tag along. That defeats the advantages of such a small, light unit. I can pop this in my pocket and forget that it's there.
Some good ideas in your posts, thanks.
I had thought about a few, some were novel thinking. 🙂 I fear than anything done outboard would either be too big to be practical or cause too much crosstalk.The seller has refunded my purchase and told me to keep the recorder. Too bad, as it's a clever little unit, has long battery life and is super easy to use. The Sony ICD-PX470 is the logical step. But it's $18 more, is larger, has a lot less memory and doesn't have a rechargeable battery. But it does do stereo on the mic input according to one Amazon reviewer who tested it with a Sony stereo mic.
Those are the BIG ones. I started with those and liked them. They don't have much top end IME, but still sound good. Very good output level and S/N. I also have the 8mm and 6mm versions in the HD series.
I finally did manage to get an impulse response using mics placed in my ears that I now use to do virtual space for headphones. It took a lot of tries, but it works and is sometimes uncanny. For that I used the last pair of my Panasonic 6mm capsules in vinyl tubing. They are rugged and fit snuggly into my ear canals. If you can get silicone tubing it's much softer and more comfortable. It's like wearing earplugs, of course, and blocks sound coming to your ear. For my "sonic snapshots" I'm using "ear loop" type holders that put the capsule just in front of the ear canal and don't block my hearing. And they need generous windscreens, as without them outdoors there is far too much wind noise. I have foam and fuzzy dead cat types of the appropriate size.
Why not integrate the microphone pre-amp into the microphone itself. SMD components should make this fairly easy. Battery size is the one issue that is harder to address.
I might. If I use a little SMD stereo mic amp that runs on 3V a coin cell like a cr1025 could be used. It ought to last awhile. Should all be small enough to go inline.
Use a cell phone battery from a small one, like Nokia BL-5.
You can even hack the housing if needed, off a scrap phone.
Battery charge control chips are easily available.
So you will end up with something that can be charged with a regular charger, and the BL-5CA battery was above 1000 mAh IIRC.
You have many choices there for batteries.
You can even hack the housing if needed, off a scrap phone.
Battery charge control chips are easily available.
So you will end up with something that can be charged with a regular charger, and the BL-5CA battery was above 1000 mAh IIRC.
You have many choices there for batteries.
Experiment to see if you need a microphone amplifier:
Make a recording with the left line input open and at maximum gain
Make a recording in silent surroundings with the microphone connected to the left line input, still maximum gain
Compare the noise levels of the left channels of the recordings (after applying the exact same amount of digital amplification to both, if needed)
If the noise floor increases more than 6 dB when the mike is connected, you lose less than 1 dB of signal-to-noise ratio by not having a microphone amplifier.
Make a recording with the left line input open and at maximum gain
Make a recording in silent surroundings with the microphone connected to the left line input, still maximum gain
Compare the noise levels of the left channels of the recordings (after applying the exact same amount of digital amplification to both, if needed)
If the noise floor increases more than 6 dB when the mike is connected, you lose less than 1 dB of signal-to-noise ratio by not having a microphone amplifier.
I was considering this as a mic amplifier to experiment with; https://www.ebay.com/itm/373738484484. Based on this https://www.maximintegrated.com/en/products/analog/audio/MAX9812.html
Looks like the chip does it all.
Looks like the chip does it all.
It does, but it also generates a lot of noise. The 40 nV/sqrt(Hz) of the amplifier itself is still below the output noise of the microphone capsule, but the 100 nV/sqrt(Hz) of the bias supply is not. There is essentially no suppression from the bias supply to the microphone output unless you insert some kind of filter yourself.