Audacity record level vs. EMU 0404 input level control

[pcneal]

I am using a EMU 0404 USB 2.0 external interface in conjunction with Audacity 2.05 to record my LP collection. I have adjusted the analog input on the EMU to insure the input levels are below clipping. The EMU has a soft-clip function to help minimize the distortion associated with hard clipping. I have the EMU/Audacity interface to record at 96KHz and 32bit Float, and all seems to be working well, However, in setting up Audacity, I have to adjust the input volume level to near zero (actually 0.07) to insure signals remain below clipping. Can anyone tell me what this Audacity record input level control actually does to the signal. If I have the analog level set to insure the A/D in the EMU does not clip, what does this Audacity record volume control actually do? My recordings seem to sound just fine, but it bothers me that I may be sacrificing some of the digital dynamic range due to this very low setting on the software record input.

Thanks,
-Parris

[kozikowski]

You can adjust sound systems so the technical specifications miss each other and get some odd results.

As an experiment, set the device for 44100, 16-bit, Stereo and then set Audacity Preferences for the same thing.

Audacity > Edit > Preferences > Devices > Stereo
Audacity > Edit > Preferences > Quality: 44100, 16-bit

Many people do sound transfers at that specification. That's the spec for an Audio CD.

Koz

[pcneal]

Thanks for you input. I will try the experiment you suggest. However, ultimately I want 96k/24b recordings for my server based streamer. I was trying to understand exactly what the Audacity record volume control did, and how that effects the dynamic range of the captured signal. I would like gain to be as far forward in the instrumentation chain as possible to maximize SNR, but I would be disappointed if Audacity's record level threw bits away by operating it at very low levels degrading the dynamic range of the sampled signal.
-Parris

[kozikowski]

Let's get it running first.
Koz

[pcneal]

Koz,
Completed your experiment, setting up EMU interface and Audacity for 44.1KHz sample rate and 16bit samples. The input level controls, the input EMU gain set at 0db (its minimum) and Audacity input level control set at 0.07 (full scale being 1.0). These setting, just as they did for the higher sample rate and bit depth, generate a seemingly good recording. These two gain settings (EMU and Audacity) act like two analog gain settings in series. If one goes up the other must go down or clipping occurs. Once again, how does the Audacity recording gain control work on the incoming signal? Does the EMU have some feedback system thru the usb port from Audacity that actually changes the analog gain, or does it work entirely in the digital domain. If digital, how does the attenuation (0.07) effect the number of bits left to represent the original signal. Thank again for your input.
-Parris

[flynwill]

The EMU-0404 has combo mic/line inputs. It sounds like you are somehow feeding the mic inputs with line-level signals.

As far as I can tell from the literature & manual the combo XLR/Phone jacks are setup such that the XLR contacts feed the microphone preamp and the phone jack is expected to be line level either balanced or unbalanced. So the question is how, exactly (with what sort of connector adapters) are you connecting your receiver or phone pre-amp to the EMU?

[pcneal]

Thanks for you input. Yes, the EMU has combo inputs, xlr and TRS 1/4" jacks. I am feeding a line level in on the the 1/4" jack with a TS jack in unbalanced mode. The EMU input levels as indicated by the led amplitude lights indicate that the signal is running about -3db on peaks with no indication of clipping. This is exactly what I would expect with a line level signal going into a line level input with the input gain set at 0db (gain 1). So the EMU is acting, I believe, exactly as expected. It is the Audacity record level input control that I don't understand. The recordings I am getting appear to be just fine, with the Audacity input level control set very low (0.07), but this low of a setting concerns me that perhaps I am throwing away bits in the recorded signal. I would just like to know how Audacity's record input level works, so that I can get the best possible recordings. Thanks again. Parris

[flynwill]

As far as I know (and the developers will hopefully chime in if I'm wrong), the Audacity record level knobs are just a front for the controls provided by the driver. They should exactly follow the knobs in the windows mixer or control program that came with the EMU.

I had a similar issue when I first connected up my Behringer UCA-202. With the default driver windows provided the software volume controls had to be set to an extremely low level. I installed the driver from Behringer and the problem vanished. I don't know if the extra gain was some feature in the chip the Behringer used that the windows default driver turned on, or if the extra gain was happening in the driver software.

Obviously your EMU is different hardware, but you might try re-installing the software package that came with it.

[steve]

I'm not on Windows, but from (many) other posts to this forum it looks like Windows often assumes that USB audio devices are microphones, and so the gain is set really high when the recording level is turned up to what looks like a 'reasonable' level.

As flynwill wrote, Audacity does not do anything to the incoming audio and the Audacity "mixer" controls (the input/output sliders) simply reflect controls provided by the computer sound system. Typically, the computer has no control over the 'analog' input gain in USB devices, but some drivers provide 'scaling' of the digital signal so as to emulate an input level control. The important thing is to set the input level on the USB device so that the device indicates a good level without clipping, then adjust the Windows controls (or the Audacity controls) so that the level in Audacity is reasonable (reported to often require extremely low settings).

Unfortunately it becomes rather complicated because there are so many different audio devices, different drivers and different sound systems, so "best settings" can vary enormously between one computer and another. You may also see differences between the settings if you switch the "Host" setting from MME to DirectSound.

More information here: http://manual.audacityteam.org/o/man/de ... .html#host
and here: http://wiki.audacityteam.org/wiki/Mixer ... es#vistacp

[pcneal]

Thanks to everyone for their input. I will do as Steve suggests and adjust the EMU front end so the input analog signal is reasonable but below clipping and just adjust the Audacity input level to where required. I really appreciate your inputs. Thanks again. -Parris