input volume with external soundcard

[donnie jepp]

Hello,

I have a question concerning the input volume slider in Audacity. I am using an external usb audio interface (E-MU 0404usb) and would like to record the signal coming from this interface without any modifications whatsoever. I can set the level of my signal with the gain knobs of the preamps of the interface and I don't want Audacity to change the volume of the (digitized) signal. It seems that in version 1.2.6 the signal is unaffected if I set the slider all the way to the right, i.e. to 1. Sliding it to the left seems to attenuate the digital signal. Is this correct? On a windows XP machine running version 1.3.11-beta the input volume slider seems to move together with the output volume slider, and doesn't seem to have any affect on the input volume (this is the way I want it to be). However, on a windows Vista pc and version 1.3.11-beta the input volume slider does work and setting it to 1 causes clipping even if the signal coming from the audio interface is far from clipping (by looking at the meters on the interface). So it seems that in this version of Audactity the digital signal is amplified. So my question is, how do I select the input volume so that Audacity doesn't change the level of my signal? By looking at the moment where the signal starts clipping both in Audacity and on my interface it seems that the value is around 0.5 but I want to be sure where it is exactly. Thanks!

Cheers,
D.

[whomper]

xp and vista seem to work differently for audacity
set xp high and lower it, set vista low and then slide it up more is what i infer works easiest.

dont touch audacity and it wont change your signal level

there is no one setting that works for all cases
sometimes you will want to move the sliders to adjust the levels
like when the signal clips then you need to lower something somewhere

how did you get the 0404 to work? i was told it had the wrong drivers to work with audacity. are you 100% positive the signal coming from it is not clipping? can you lower the levels from that interface to fix the problem?

[donnie jepp]

dont touch audacity and it wont change your signal level

Do you mean that if I start Audacity and don't touch the sliders, the level will be such that the signal level is not changed? If this is true this is the solution to my problem.

there is no one setting that works for all cases
sometimes you will want to move the sliders to adjust the levels
like when the signal clips then you need to lower something somewhere

I want to adjust the signal level on the audio interface in order to get the highest possible signal to noise ratio. If Audacity amplifies the signal afterwards, there will be a high probability of clipping since at the peak levels it will be very near to clipping levels already. If it lowers the signal level the signal to (quantization) noise ratio will be lower and there could be clipping in the interface without the Audacity level meter indicating this problem. In other words I just want to use the preamp gain of the interface to adjust the signal level and don't want Audacity to change this level.

how did you get the 0404 to work? i was told it had the wrong drivers to work with audacity. are you 100% positive the signal coming from it is not clipping? can you lower the levels from that interface to fix the problem?

The MME driver seems to works fine with Audacity. Apart maybe from the fact that my signal is limited to the range [-0.5,0.5] in windows XP (been having the same problem in Adobe Audition even with the ASIO driver, but not in other software), so the signal is always attenuated 6dB, which is very strange.

Thanks for the feedback!
D.

[whomper]

there are a number of places the signal can get amplified between the source going into the preamp to the sound card and the pc software up to the speaker out from the power amp.

but if you don't twist the knobs at any of them they will not amplify on their own. they will amplify by whatever the knob was set to.
for digital slider is equal to knob. once they are set they will do what you set them to and not turn/slide themselves.

if clipping could happen either turn down the preamp sound card or audacity.

note that if you have everything turned down in the pc and it is clipping then you will have to turn down the gain in the preamp or external sound card.

can you use the db view?
that will show if clipping occurs with a red line where it happens.
you can see also where the signal level mostly is at to see how much headroom you may have. magnify on the left of the track near the top end to get more detail.

if you record with 24/32 bits you can record low and then amplify later without messing up the S/N.

[steve]

Hello,

I have a question concerning the input volume slider in Audacity. I am using an external usb audio interface (E-MU 0404usb) and would like to record the signal coming from this interface without any modifications whatsoever. I can set the level of my signal with the gain knobs of the preamps of the interface and I don't want Audacity to change the volume of the (digitized) signal. It seems that in version 1.2.6 the signal is unaffected if I set the slider all the way to the right, i.e. to 1. Sliding it to the left seems to attenuate the digital signal. Is this correct? On a windows XP machine running version 1.3.11-beta the input volume slider seems to move together with the output volume slider, and doesn't seem to have any affect on the input volume (this is the way I want it to be). However, on a windows Vista pc and version 1.3.11-beta the input volume slider does work and setting it to 1 causes clipping even if the signal coming from the audio interface is far from clipping (by looking at the meters on the interface). So it seems that in this version of Audactity the digital signal is amplified. So my question is, how do I select the input volume so that Audacity doesn't change the level of my signal? By looking at the moment where the signal starts clipping both in Audacity and on my interface it seems that the value is around 0.5 but I want to be sure where it is exactly. Thanks!

Cheers,
D.

It sounds like you already have a pretty clear understanding of what is going on.
I may cover some really obvious points that you are already well aware of, but hopefully clarify the details that have prompted your question.

You are quite right about the volume slider being different in different versions of Audacity, and on different operating systems. The Audacity developers have a huge problem in trying to get the volume sliders to work on all platforms (Windows, Mac and Linux) and for all sound cards. In some cases it is just not possible because the sound card drivers do not support control from other applications - in other cases they use non-standard methods which are difficult to cater for.

What you are asking for is the reverse of what most users want. Usually people are asking "how can I control the input/playback level from within Audacity?" and this is the feature that the developers try to support as broadly as possible. My own thoughts on this are that while it may be a convenience to many users to have input/playback control from within Audacity, it is not a feature that I have ever relied on, prefering to use the sound cards' own interface to adjust the levels. I think Gale Andrews described this well in a recent post:
"Audacity tries to give you the convenience of a direct way to select the input source and a direct way to control the input level on the hardware. This isn't always easy, and for it to work it is very dependent on the sound device having up-to-date drivers meant for the particular operating system and computer model, and made by the motherboard or device manufacturer" (Documentation page on upgrading drivers http://wiki.audacityteam.org/index.php? ... ce_Drivers )

An issue that will be of concern to you is how Windows Vista controls sound volume. There have been a number of posts both here and on the developers mailing list about "Direct Sound" drivers "scaling" the digital audio rather than adjusting the analogue gain level. This is not good for high quality audio recording as it raises the digital noise floor and reduces the available dynamic range - exactly the concerns that you are voicing. As I understand it, it is for this reason it is usually better on Vista to use MME rather than Direct sound. Apparently you are already using MME, but to check, look in Audacity; "Edit menu > Preferences > Devices". This will usually be of more relevance to users of internal sound cards, as will become apparent in a moment).

The order in which you set levels is important to maximise sound quality. Start at the sound source and work your way along the signal chain:
Sound input (microphone) > | pre-amp > A/D | > sound card drivers > Audacity > Hard Disk

The signal level from the sound input should roughly match the input capability of the pre-amp - so microphone into the mic socket of the pre-amp, line level input into the line input of the pre-amp. Some pre-amps have switches to set the approximate range of the sound source - for example a switch for "Mic/Instrument".

What happens between pre-amp and the analogue/digital converter you have little control over as it's all inside the same unit - all you can do is to adjust the pre-amp gain so that you get a good signal that does not distort/clip.

With a USB device, the "sound" entering the computer is already in digital form. Depending on the sound card drivers, the input level adjustment of the sound cards interface may be able to change the sound cards input gain. On all of the USB devices that I have used this is not the case and the input gain has been entirely controlled by the hardware input level knob on the USB sound card.

From that point on, everything is digital scaling, so it is just a matter of setting each level control so as to avoid clipping. On my current USB sound card on Win XP, the optimum results are with all sliders on max. On a Vista machine I have to turn down the recording level in the "Sounds" section of the Windows Control Panel, then everything else on max. With my previous USB sound card, best results were with everything set to 0.7 (70%) and the Audacity record level slider was unavailable (greyed out).

On Vista it is certainly worth checking in the Control Panel - there are sometimes additional settings hidden away in there that are not available elsewhere. This article provide some additional information about sound settings in Vista: http://wiki.audacityteam.org/index.php? ... ng_sources

One final tip/suggestion - don't underestimate the importance of the sound card drivers, they can have a massive impact on sound card performance. If you are experiencing problems or quirks with the sound card it is worth checking if updates are available for your sound card drivers. Driver updates are usually made available on the manufacturers web site.

[donnie jepp]

Seems like there is no simple solution to the problem. Anyway, thanks a lot for your explanation.