USB microphone

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Gus

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http://namm.harmony-central.com/WNAMM05/Content/Samson/PR/C01U.html

Look at the price.

I don't like the CO1 however the CO1U donating its A/D USB parts to another microphone could be a fun thing for a laptop based.................................................................
 
What is the power spec for USB? Another question would be what can you realy get from a laptop or desktop power wise from usb?

If we can get a 1/4 to a 1/2 watt of power. I think a tube circuit could be possable.

DC to DC converters and a nice tube ........................................
 
[quote author="zebra50"]looks like a lot of fun

...now how to drive a tube from USB power? :grin:[/quote]

hehe, g7 usb!
 
possibly useful website - will take a few minutes to pull out the usefl bits...

http://www.usb.org/developers/docs/
 
I managed to get this out of the archive on the above site but am not sure which values to pick.
If you have a highpower hub then is it 500 mA at 5 V ?

Also, this is for USB1.1. I couldn't open the USB2 file.


Supply Voltage:
High-power Port VBUS Note 2, Section 7.2.1 4.75 5.25 V
Low-power Port VBUS Note 2, Section 7.2.1 4.40 5.25 V
Supply Current:
High-power Hub Port (out) ICCPRT Section 7.2.1 500 mA
Low-power Hub Port (out) ICCUPT Section 7.2.1 100 mA
High-power Function (in) ICCHPF Section 7.2.1 500 mA
Low-power Function (in) ICCLPF Section 7.2.1 100 mA
Unconfigured Function/Hub (in) ICCINIT Section 7.2.1.4 100 mA
Suspended High-power Device ICCSH Section 7.2.3 ; Note 15 2.5 mA
Suspended Low-power Device ICCSL Section 7.2.3 500 mu-A

I think this could be a really interesting project!
 
[quote author="Marik"]What is the standard for audio digital output for USB? What about gain control?[/quote]

Good thinking - should be some stuff here

http://www.usb.org/developers/devclass_docs/

I'll look more later - need food!

Stewart
 
Looks like 5 V at .5amps for 2.5watts per port If I understood the intel PDF.

5V for the fil supply might be to low an underheating voltage for a ef86
so using the 5V for a "standard" 6.3 at 150ma might not work

A 1.25V fil tube feed via an RC voltage dropping string the R for the drop and the C for filtering noise and a DC to DC converter for the B+ and capsule voltage might be fun like the DI Thomas H. built.

Yes there are other tubes.
 
Actually, my immediate thinking was to convert it into SPDIF output, and use external PSU.

Here is USB pinout:

http://www.vpi.us/technote.html
 
quick thought --- TAS1020 has been used a lot in some stereo I/O units with added funcionality. (i.e. phantom on off switches etc).

I don't know too many of the details, but if you guys want to have a look at the device and fire some questions, i'll be glad to answer them


Cheers
R
 
I reached the same conclusions as Gus with respect to voltage and current. That's a best case scenario.

And I cracked open a powered USB 4-way hub (belkin). It runs off 7.5V wall wart and contains a 7805 regulator.

BUT...

It meters out at only just over 3V. I hooked up a submini pentode heater (7 ohms-when-cold, 150 mA rated) to one of the US cable outputs and the voltage dropped to 0.000V. It can't deliver current.

Maybe the blekin is crap and my macs can deliver closer to 5V, but I'm not ready to try that yet!

Any better experiments? It's getting late here and I have to work tomorrow. Look forward to reading this thread in the morning.

Stewart

PS Rochey - thanks for the pointer. Will check it out tomorrow. :thumb:
 
Not too long ago I reviewed a USB boundary layer microphone by Beyerdynamic. It used a chip by AKM which is a combination of a preamp, AD converter and USB interface. The chip's number was AK5370. Maybe Samson use the same chip. If yes, the audio performance won't be super professional. It was all right for the Beyer microphone, because it was designed for office use, e.g. with dictation software. But perhaps there's better chips by now. The AKM chip is fairly old - there was a driver already on the Win98SE CD.
 
Rossi

thanks for the information.

here is a link

http://www.asahi-kasei.co.jp/akm/en/product/audio.html

If it is the chip you posted it is only 16bit
 
Yes, it was 16 bit. S/N was somewhere in the 70s or low 80s if I remember correctly, so 24 bit wouldn't have made sense anyway. It's not a chip for "serious" audio. It's a handy chip for "okay" audio.
 
there are integrated TI devices (PCM290x) - but these are typically 89dB SNR.

Ti has the PCM4201 (50mW 112dB single channel ADC) being released this year that's designed with the wireless mic in mind. Maybe that with a tas1020 would be a nice little solution? The low power of the device fits nicely with the crappy powering solution that USB has :?

again, if your interested, ask -- otherwise, just consider as as FYI :thumb:
 
The PCM290x chips look pretty okay for what you could possibly do with a USB microphone. Don't forget that a USB interface means that you have to switch to its driver in your DAW, and usually you can use only one driver at a time. With a USB microphone that means you have no playback channel. You can't record overdubs with a USB microphone. I wonder if Samson thought about this. But it may be handy for field recordings with a laptop or interviews, bootlegging, whatever.
 
[quote author="Rossi"]Yes, it was 16 bit. S/N was somewhere in the 70s or low 80s if I remember correctly, so 24 bit wouldn't have made sense anyway. It's not a chip for "serious" audio. It's a handy chip for "okay" audio.[/quote]
I am i pretty out in the modern digital system, but
what difference in dynamic range is between 16 an 24 bit
codecs?
I read the catalogue and dynamic range is between 70 and 80 dB in
16 bit codecs and between 90 and 100 dB in 24 bit codecs.
If I compute bits, I get: 24 - 16 = 8. and 6*8 = 48.
Why 24 bit codecs have not 130 dB dynamic range ?
And is that 90 dB some barier in dynamic range, which can be
handled by (standard) semiconductor equipment ?
And if we can headroom 15 dB, useful dynamic range is only 75 dB ?
and what about dynamic range of mic signals ?
If some mic have 15 dB self noise, and signal in fortissimo is 100 dB,
dynamic range of all signal without compression is 85 dB.
For that dynamic 18 bit ADC is enough.
And I mean, that good 18 bit ADC is touching the analog signal
limitation and difference in the dynamic range can be 10 dB between
16 and 18 bits, and is nothing between 18 and 24 bits.
It is maybe reason, why best analog-devices SAR converters are 18 bits.
The only usefullnes of low significant 6 bits in 24 bit AD converter is
for random generator.
There are only two ways to improve dynamic ratios of chips.
1) to made chip with 100 V input signal range (it is impossible because
of parasitic thyristor in semiconductor structure)
2) to made chip with 500 mA range current input. It may be possible,
but every designer want device with voltage input and digital output.
(If it is the only reason why nobody made it, I will manufacturing it.)

Then we will still buy on paper 24 bit chips with 18 bits effective.

What is real on 24 bit "proffesional" mania. For nearly all recording
16 bits is enough, 18 bits are top.

xvlk
 
Well, I'm not saying 16 bit isn't professional *in general*, but the AK5370 in particular was never meant for serious studio purposes but for computer acessories etc. Remember, it's not just an ADC there's also an on-chip preamp of so-so quality

There are in fact some soundcards (such as EMU 1820m) that are close to 120 dB dynamic range. That's still not full 24bit (144 dB), but it's more than 16bit converters can handle. And with most DAWs, there's only 16 and 24 bit file support. So no inbetween numbers like 18 bit. And hard disk space is cheap these days.

But I agree, it's very hard to actually get more than 90 dB SNR in practice.

Btw. take a look at Neumann's Solution D microphone. Or the manual, that is. It's verrrrry expensive. Since the dynamic range of a good microphone capsule is 130 dB and above, even 24bit may not be enough sometimes.

That said, a noise floor at -96 db (i.e. 16 bit) doesn't sound noisy to me.
 
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