Computer Audio Asylum

RE: Squeezebox vs. EMU 0404 USB as Transport for SPDIF

67.164.165.165

In Reply to: RE: Squeezebox vs. EMU 0404 USB as Transport for SPDIF posted by Dawnrazor on February 06, 2008 at 19:07:14

Do you adjust the volume with your software, or does the emu output a full unattenuated signal? and the benchmark or further up does the volume?

Hi Dawnrazor,

The only digital volume adjustment I do is in the Berhringer unit itself, to avoid digital clipping due to the digital filtering it provides (for the bass only). When this occurs, it's very audible as a crackling sound, but can be eliminated easily by looking at the VU meters of the Behringer, which have a digital clipping indicator, and adjusting the digital level to prevent the clipping. To help with that, I use a reference CD (Miles Davis' "Milestones" - the track "Two Bass Hit"). This song is recorded very loudly, and shows up digital clipping clearly on the Behringer's VU meters. I adjust the Behringer's digital volume control for the minimum attenuation that avoids digital clipping. This ends up being about 2 dB with my setup.

I have disabled the front panel volume control on the Benchmark, and instead use the volume control of my preamp, which can be controlled using the remote. However, I still use the multi-turn volume control trimmers on the Benchmark's real panel as follows:

1) To reduce overall volume such that the remote volume control of my preamp is in a range where it's not jumpy.

2) To get matched volumes between channels at a typical volume setting.

I do the first step empirically. I determine where the preamp's volume control needs to be set in order to get good control with the remote. Then I do a coarse tweak with the Benchmark's rear-mounted trimpots to get close.

To get precise channel matching, I first set the preamp's volume control to match that of typical listening. Then I play a mono WAV file of a sine wave of about 500 Hz. Using an AC voltmeter, I match the measured voltages of the preamp's left and right outputs with the voltmeter by varying the adjustment of the Benchmark's multi-turn pots in back. I can get channel-to-channel matching within hundredths of a dB at the normal listening level. This is possible even with a cheap AC voltmeter, as long as the display is digital (so you can read to the desired resolution).

In practice, this works great. Matching the two channels like this eliminates the "audiophile nervosa" effect from channel mismatch of conventional preamp volume control pots. Integrated circuit control of volume has better matching than motorized pots, but depends on using MOSFET switches in the IC, which cause distortion. The best approach is multi-position switched attenuators, but these get complex and expensive. Using a preamp with a motorized pot, combined with individually adjustable outputs of the DAC, works well for me as an economical solution. YMMV.

Follow Ups:

Ok. Here is a player that MIGHT work - Dawnrazor 21:41:56 02/06/08 (1)
- RE: Ok. Here is a player that MIGHT work - andy_c 16:41:07 02/07/08 (0)

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