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No Recording Volume Adjustment for Ion TTUSB05 and AT USB Turntables, Two strikes: No pre-ADC gain, no software volume level
Knowzy
post Feb 14 2009, 02:59
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As we previously discussed, few USB turntables offer gain adjustment before the signal hits the A/D converter (see chart #2 in the USB Turntable guide for specific models).

Here's what I didn't expect: There's no way to adjust the recording volume in Windows Mixer or Audacity.





"USB Audio CODEC" Screenshots







A Regular Sound Card




Of course, you can always normalize after you're done recording. Nonetheless, I expected to find a slider in Windows Mixer, just like any other sound card.

This could just be a limitation of the Microsoft's USB Audio CODEC driver (USBAudio.sys). I'm curious if Mac and Linux users have the same limitation.

Then again, I tried Ploytec's USB ASIO driver and got the same results, so maybe it's the nature of the hardware.

In the end, I guess you can always spin it in marketing terms: It's a feature- you never need to set your levels!



A Sample Clip
With that, I present my first USB turntable sample from the Audio-Technica AT-LP2D-USB. It is the first track from the Ultimate Analogue Test LP.

This 1kHz test tone is used for, among other things, setting the recording volume to read 0VU. Obviously, I cannot do this without post-processing.

BTW, the first 10 seconds are the sounds of the tonearm automatically placing itself on the record.

Many more samples are coming this weekend.



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Knowzy
post Feb 16 2009, 22:02
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QUOTE (AndyH-ha @ Feb 15 2009, 18:44) *
Line level inputs don't go through a preamp on very many professional cards, although some of the "external audio interfaces" have full analogue mixing facilities built in. These will frequently have some way to route the line level input so at to least reduce input amplitude (in the analogue domain).

You seem to be confirming what I assumed: With the possible exception of some high-end sound cards, the so-called "Recording" volume you see in Windows Mixer is post-ADC (at least on the Line-in).

It's perhaps useful for bringing the sound up from a low level. However, it is useless for eliminating clipping due to a strong signal on the analog side of the A/D converter.

The fact that it is missing in Windows Mixer is of little consequence to making useful adjustments to the recording volume of a USB turntable.


QUOTE (AndyH-ha @ Feb 15 2009, 18:44) *
The normal approach is an analogue mixer before the soundcard that can be used to make adjustments before the soundcard input...With a direct USB input, and no way to get at the signal between production (in the cartridge) and the A to D, still inside the TT, you are screwed.

A handful of USB turntables insert a gain knob in the circuit between the pre-amp and A/D converter, generally on DJ USB turntables. The Pro-Ject Debut III USB does not have adjustable gain.

This inexpensive part could save USB turntable makers a lot of grief from users who encounter clipping. Customers who don't know any better or don't care could leave the gain knob in its default position.

QUOTE (AndyH-ha @ Feb 15 2009, 18:44) *
One would think that it would not be too hard for the USB TT designer to have calculated what levels might reasonably be expected from LPs and made the phono preamp gain accordingly, so no clipping could occur, but that doesn't seem to be the case with your particular sample.

Of course, this is a balancing act. Set the levels too low and you might lose audio data from weak signals. Again, more the reason to give the user the ability to make the adjustment him/herself.


QUOTE (AndyH-ha @ Feb 15 2009, 18:44) *
I suspect your belief that the cartridges are non-replaceable is just an misinterpretation of what you see. I've never seen or heard of such a thing.

Actually, this comes straight from my conversations with Audio-Technica.

We're talking about record players of $150 and less. There's no standard mount or any screws at all. The counterbalance is fixed. There is no anti-skate adjustment.

I suppose you could chisel away at the plastic until you got the cartidge off and somehow affix the leads to a new cart, etc. but that's quite a hard hack for a TT that isn't worth the effort! smile.gif
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