OK. So I am just dipping my toe into the murky waters of PC-based audio, in order to do some before/after measurement of some amplifier upgrade work I'm doing.
I saw that folk are using 'PC soundcards' and software such as 'RMAA' to do this, so after a brief bit of research I acquired an EMU 0404 PCI, which I've just installed into a Windows 7 PC.
My very first task was to assess its output, so I hooked up my old oscilloscope and HP AC Voltmeter, and downloaded an audio signal generator application. I used a 600ohm terminator, and set the output level to 0db/0.775v using the main mix slider in 'Patchmix DSP'.
I am seeing a distinct HF cutoff above ~16kHz. It's down by 3db at ~18.5kHz and ~7db by 20kHz.
I can't see any filtering configuration in Patchmix, nor in the Windows sound control panel.
Either the card is faulty or there's some software nonsense going on ? Any pointers welcome...
Andy
I saw that folk are using 'PC soundcards' and software such as 'RMAA' to do this, so after a brief bit of research I acquired an EMU 0404 PCI, which I've just installed into a Windows 7 PC.
My very first task was to assess its output, so I hooked up my old oscilloscope and HP AC Voltmeter, and downloaded an audio signal generator application. I used a 600ohm terminator, and set the output level to 0db/0.775v using the main mix slider in 'Patchmix DSP'.
I am seeing a distinct HF cutoff above ~16kHz. It's down by 3db at ~18.5kHz and ~7db by 20kHz.
I can't see any filtering configuration in Patchmix, nor in the Windows sound control panel.
Either the card is faulty or there's some software nonsense going on ? Any pointers welcome...
Andy
What is the samplerate set to?
I get essentially flat response out to 20K on loopback with samplerate of 96k (Which is what I use with this card). The SOS review was also quite flattering, however in that case a simple loopback cable would have been used, without termination resistors. Link - Emu 0404
Have you tried terminating with a higher value resistor? Are the cables sufficiently low capacitance? At 600 ohm even small cable capacitance can cause major droop. I doubt it is a software issue - the one thing to check though is that you operate in ASIO mode only, as W7 can do some funky things with resampling when running in shared mode.
I get essentially flat response out to 20K on loopback with samplerate of 96k (Which is what I use with this card). The SOS review was also quite flattering, however in that case a simple loopback cable would have been used, without termination resistors. Link - Emu 0404
Have you tried terminating with a higher value resistor? Are the cables sufficiently low capacitance? At 600 ohm even small cable capacitance can cause major droop. I doubt it is a software issue - the one thing to check though is that you operate in ASIO mode only, as W7 can do some funky things with resampling when running in shared mode.
I think your last point hit the nail on the head, I checked the settings in one of the apps (Visual Analyser) and the sample rate and bit depth weren't in sync with the driver. Oops. VA is doing some weird stuff, the amplitude annoyingly flobbers about all over the place when using the slider to adjust frequency.
I distrust Windows as a platform for this already...
I distrust Windows as a platform for this already...
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