AndyH
Posts: 1425
|
 Posted - Sat Jun 14, 2003 12:42 am
|
|
|
A few questions arise from my first experiment with microphone recording. For this I recorded from my living room speakers, with a single microphone set up on front of my normal listening position, pointing towards what I perceive as the center of the sound stage.
This was not oriented towards the subject of my earlier post about comparing subtle differences in equipment by recording the output via microphone. I simply needed some source to record, so I put some Sara K on the CD player and listened to the same song over and over as I tried to get things working.
Various times I seen written here that CE's VU meters are dependent on the soundcard driver, that they can only report what they are told, whether it be right or wrong. Most of my recordings are of LPs, directly off the phono section. I've never had need to pay much attention to the VU meters because that input just happens to be right where it needs to be. With the microphone input, clipping was easily (in a manner of speaking) obtained, so I noticed some things I never looked for before.
First, when I adjusted the input level so that the highest peaks just reached 0 on CE's VU meter, with the clip indicator never coming on, the recording still had lots of clipping, which does not sound very good. Bring up the soundcard control panel, I frequently saw clipping indicated thereon (with no clipping on CE's meters). Although the soundcard meter display is much smaller than CE's, and thus not so easily fine tuned, it should not be a problem to use it, but I am curious. Is this discrepancy between the card's VU meters and CE's VU meters normal?
I have both an Audiophile 2496 and a recently obtained Mia in the same machine. The first music recording with the Mia was an LP, via its analogue input. The next day I recorded the same LP into the Audiophile to compare results. (This is obviously not about microphone recording, but somewhat relevant). At first I thought the recordings sounded significantly different, but I soon realized that the Audiophile recording was louder. The RMS average difference was only 1.5dB, according to CE, but my general impression was of a more extreme difference.
For most of my microphone tests, I used the S/PDIF output of the M-Audio DUO (the microphone preamp) running into the S/PDIF inputs of the Mia and the Audiophile. The connection was via a cable that is supposedly high quality and made specifically for this purpose (i.e. not simply an analogue audio interconnect cable). Recordings were at 32/88.2. The DUO is switched to standalone mode for S/PDIF output, and the sample rate is set by hardware switch.
I set the input so that CE's VU meters were running just up to 0dB on the highest peaks, no clipping indicated, recording via the Mia. This produced a recording that actually peaked at -6dB (CE's statistics), but that had many clipped samples. The clipping was observable in CE's Edit view by virtue of the fact that many peaks reached this -6dB level, and in that these peaks looked sort-of squared off. In Spectral view these peaks showed many click-like spikes that went all the way to the 48kHz Nyquist limit.
When I switched the input cable to the Audiophile, but changed no external settings, CE's meters now showed frequent clipping (which they had not with the Mia). The resultant recording had a much higher general level than the Mia's recording, and showed much clipping at 0dB in CE's edit view. This was probably due to different settings in the soundcard's control panels, but the difference in the LP recordings was not due to the same thing.
The above stuff is mostly just curiosity. I realize that my two to three hours of experimentation, the first time I ever used a microphone, cannot begin to compare with the experience necessary to make good recordings. It is just my way of getting started. There is one thing more serious, however.
In order to get a useable recording level, I had the DUO's level control(s) set almost at maximum. This preamp is supposed to provide 60dB of gain. The gain is not calibrated, but there are division markings behind the knob. Based on 1/2 circle being divided into six parts, with one more division beyond 180 degrees in both directions, the scale extends through 240 degrees. The knob actually moves a little beyond both ends of the scale.
CE doesn't register anything with the gain set below the last division, and even then the signal level is very low unless the knob is almost at the end of its travel. In the test I described above, the Mia did not indicate clipping in CE (but did on its own meters) and the Audiophile showed frequent clipping on CE's meters. Using the Audiophile, I backed off the preamp's gain control so that the Audiophile meters stopped clipping, which also caused CE's meters to fall significantly.
Adjusting as carefully as possible to avoid going too far down, I actually barely moved the gain knob at all. It was in fact so little that I could not be certain, from touch, than any movement occurred, but the VU meters said it had. On the Audiophile's meters, the peaks fell from frequent clipping to mostly below -6dB. The resultant recording had one peak at -3.5dB, one at -4.5dB, and everything else much lower. Surely this is not normal behavior for a microphone preamp?
I also did a little recording via USB. This only worked in CE at 44.1 (I thought I had recorded at 48kHz some time ago, but I could not now get any signal in CE except at 44.1). Gain control on the DUO had to be near maximum with USB, just as for S/PDIF, although I did not try to make any measured comparisons.
To answer a few potential questions. The Hi/Fi was set to my normal listening level. This may be lower than in a studio recording, but Sara K. sounds about right to me, as far as I imagine how loud any half-way normal person might sing. The DUO has one green LED for signal, and one red LED for clipping. The green LED flashes occasionally. Within those few degrees of gain control that are actually useable, I can turn it up high enough that the red LED flashes on the loudest peaks.
During the 6+ minute recording that produce the -3.5dB maximum, I went down the hall and into the back room to make a phone call. At the end of the song, as it faded out, my normal level phone speaking was recorded along with the Hi/Fi speaker output (although at a lower level) -- that from behind the microphone.
The Mia's control panel was set for +4 for these experiments. I did try -10 at first, but I think that was before I realized I needed to turn the preamp gain up all the way, so I may not have actually record anything at that setting. I never though of it after finally getting a signal to register at the computer and beginning recording. For the LP recording, the Mia was set at -10. The Audiophile input has no level options; it should be more or less equivalent to the -10dB level, I think. I can see the Mia's setting making a difference for the microphone recordings, but not for the LP recording.
The DUO has switches for +4 and -10, both input and output independently. Those apparently do not effect the S/PDIF output, although switching while recording does produce clicks. The manual says they effect the line input and line output.
There are -20 dB pads on the DUO (one per channel). Pressing those switches does reduce the input level, but I did not attempt to measure how much. Likewise, the microphone itself has a -10dB pad switch. That also works; it reduces the level. Except for brief tests to see the effect, I did all recording without the pad reductions.
Most of the recordings were done via microphone channel 1, but I did try channel 2. It seems to be identical to 1 as far as needing near maximum gain to produce a useable signal.
|
|
|
|
All Forums
microphone, DUO, Mia, Audiophile
Topic 
