On Thu, 3 Aug 2000, David W. Tamkin wrote:
> | Unfortunately I have no way of getting the SPDIF back into the computer
> | again so I'll have to rely on the MD's level meter.
>
> With no digital ports on my soundcard, the only way I can get the data back
> into the computer is to copy the MD to CDRW and rip from the CDRW. Now if
> only I could get a few unpestered minutes to try it! (It involves recon-
> necting cables and other such steps that demand clear thought.)
Ah, but I can't get it from the MD to the CDRW because my CD-recorder is
on my computer.
> | What I'll probably do is feed it with a ~250Hz tone so the level is stable.
> | If I don't get a horrible headache I will post the results :)
>
> Please don't get the headache, and please do share the results.
OK... I have been fiddling with the tone generator for about 2 and a half
hours now.
My Setup:
XMMS Version 1.2.2 Tone Generator Plugin (it's just an "x = a sin wt" sine
wave generator)
Soundblaster 16 Sound card with homemade digital output board
Homemade coaxial cable
Sony MDS-JE520 MD Deck (ATRAC 4.5)
Sony coloured MD (red) [no, I haven't tried it with other colours :)]
What I did and what happened:
<keep-out-of-trouble>
DISCLAIMER: I cannot guarantee the accuracy of these results. They may be
due to another part of the hardware, not the monauralizing algorithm in
the MD recorder.
</keep-out-of-trouble>
First, I tried a 250Hz tone as I had said in my previous email. I checked
the tone generator plugin source code to ensure that both channels would
be identical (the code is in C, email me or see http://www.xmms.org/ if
you want a copy, the plugin is included in the main xmms package), which
they were, and ensured that the MD was recording in mono with the level
set on 0dB (flat) on both the MD deck and the sound card. This caused the
tone to register at full volume (the 0dB mark on the MD's level meter).
I recorded a short ten-second burst of this tone, and played it back.
However, no noticable volume loss occured.
So, I tried increasing the tone frequency. Here are the results (all
done using short ten-second recordings) :
Frequency/Hz | Number of level meter bars below 0dB
---------------------------------------------------
250 | 0
1000 | 0
2000 | 0
3000 | 0
4000 | 0
5000 | 1
6000 | 1
7000 | 1
8000 | 2
9000 | 2
10000 | 2
11000 | 2
12000 | 3
13000 | 3
14000 | 4
15000 | 5
16000 | 6
17000 | 7
18000 | 7
18500 | 8
19000 | 9
20000 | 10
Note: The level meter scale is *not* linear
For reference the meter has 18 bars from "negative infinity" to 0dB on
each channel (plus one larger one for 'over'). The numbers in the table
are the number of unlit bars from and including the 0dB bar (the 'over'
bar didn't light up at any time).
I thought that this frequency response may be due to the MD's ATRAC so I
reran the entire test with stereo recording. The meter remained on 0dB.
No noticeable volume loss occured even at 20kHz.
Conclusion:
The volume loss appears to be frequency-dependant, as the frequency
increases, so does the loss in volume.
Due to the amount of home-made hardware involved I think it would probably
be best if somebody else (David?) tries this as well (using a different
tone generation program) to see if we can get similar results, before we
start to draw any real conclusions / blame Sony.
Next puzzle: how do we explain this?
Jonathan
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