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Recordings of Fuze+ noise, nothing playing, and playing silence
skamp
post May 3 2013, 11:02
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These are recordings of my Rockboxed Fuze+ playing nothing, and playing a digitally silent file.
Attached File(s)
Attached File  fuze_nothing_playing.flac ( 1MB ) Number of downloads: 71
Attached File  fuze_playing_silence.flac ( 1003.52K ) Number of downloads: 69
 


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stv014
post May 3 2013, 17:04
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It would be possible to find out more if the following were known:
- the voltage corresponding to the 0 dBFS level of the recording (it has -97.509 dBFS A-weighted noise on the left channel, and -97.161 dB on the right, but relative to what ?)
- the voltage at the full scale output of the player, or a recording of a tone played at a known dBFS level, for calculating the actual SNR
Other possibly useful information:
- noise at different volume control settings (minimum vs. the maximum at which a 0 dBFS tone is not clipped)
- noise of the recording device itself
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skamp
post May 3 2013, 17:22
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Here's a recording of the Fuze+ playing a 1kHz tone at 0dBFS and at max volume (0dB with Rockbox), with the exact same recording conditions as the other files (same volume calibration, loaded with the Shures). HTH

This post has been edited by skamp: May 3 2013, 17:23
Attached File(s)
Attached File  tone.flac ( 1.33MB ) Number of downloads: 51
 


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stv014
post May 3 2013, 17:32
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That gives about 96.3 dB (A-weighted) SNR, but it is still not known what the output voltage is at 0 dBFS. But if it is ~1 Vrms, and the noise does not decrease much at lower volume settings, then the ~15 uV noise voltage can indeed be audible with some sensitive IEMs like the Shure SE425, which needs 20 mVrms for 90 dB SPL (measured by InnerFidelity), so 15 uVrms translates to 27.5 dB A-weighted SPL.

There is no significant difference between the 'nothing playing" and "silence" files.

The "tone" file has -64 dB THD+N on the left channel (unweighted), and -61.4 dB on the right. With the tone playing, the noise floor rises to about -75.6 dB (A-weighted) on both channels, indicating some DAC noise modulation.

This post has been edited by stv014: May 3 2013, 17:46
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bennetng
post May 3 2013, 17:53
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@skamp

You need to turn the recording gain higher when recording your portable player (compared with looping the 0204) to achieve an optimal RMAA recording level right?

Try to use the same recording gain level as if you are recording the portable player, and decrease the output level of your 0204 to perform a loopback test, this should show the true limit of 0204's recording quality. Please record in 24-bit and post the report.
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stv014
post May 3 2013, 18:17
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QUOTE (bennetng @ May 3 2013, 18:53) *
Try to use the same recording gain level as if you are recording the portable player, and decrease the output level of your 0204 to perform a loopback test, this should show the true limit of 0204's recording quality. Please record in 24-bit and post the report.


Better yet, just record silence (shorted input) with the 0204 at the same settings as what was used for testing the Fuze+, and post that file as well. A low volume recording from the Fuze+ (again at the same recording settings on the 0204) would be useful as well, to see how the absolute noise level changes. Finally, the voltage of the tone could be measured with a DMM (at a lower frequency if necessary) to allow for converting the levels to Vrms or dBu. What is most relevant to hiss with IEMs is the noise voltage at low volume settings.
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eahm
post May 3 2013, 18:48
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Do you turn off the screen when you record? My e250 I just got from a friend makes noises when the screen is on.

This post has been edited by eahm: May 3 2013, 18:48
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skamp
post May 4 2013, 10:40
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Screen was on.

I couldn't record the EMU's line out with the Fuze+ input gain because there's no volume control on it. I tried recording the headphone out but there was some significant channel imbalance.

First, I plugged the EMU's line out to its line in, and recorded with nothing playing, and with silence playing (with the same Fuze+ input gain).
Then I recorded the Fuze+ with nothing playing, and with silence playing, at -12dB, -24dB and at -36dB in Rockbox (loaded with my Shures).

HTH
Attached File(s)
Attached File  emu-nothing.flac ( 843.59K ) Number of downloads: 46
Attached File  emu-silence.flac ( 843.01K ) Number of downloads: 50
Attached File  fuze-nothing-12dB.flac ( 911.85K ) Number of downloads: 42
Attached File  fuze-silence-12dB.flac ( 911.95K ) Number of downloads: 41
Attached File  fuze-nothing-24dB.flac ( 895.23K ) Number of downloads: 40
Attached File  fuze-silence-24dB.flac ( 895.22K ) Number of downloads: 43
Attached File  fuze-nothing-36dB.flac ( 888.39K ) Number of downloads: 45
Attached File  fuze-silence-36dB.flac ( 888.49K ) Number of downloads: 40
 


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stv014
post May 4 2013, 12:29
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QUOTE (skamp @ May 4 2013, 11:40) *
First, I plugged the EMU's line out to its line in, and recorded with nothing playing, and with silence playing (with the same Fuze+ input gain).


It would be better to record the noise floor of the line in only, because the quality of the line output of the EMU is not really relevant to testing the Fuze+. That way, the noise levels could be compensated for the EMU noise. But even if the full loopback noise power is subtracted (which gives an optimistic estimate), there is only a ~2 dB improvement in the -36 dB "silence" case:

CODE
      Tone     Fuze+     Fuze+     Fuze+     Fuze+     EMU       Fuze+
      0 dB    silence   -12 dB    -24 dB    -36 dB   loopback  -36 comp

L:   -1.117   -97.509   -99.638  -100.398  -100.546  -104.494  -102.785
R:   -0.868   -97.161   -99.697  -100.134  -100.302  -104.341  -102.481


All the values in the above table are A-weighted dB relative to 0 dBFS in the recording (so a constant input gain is assumed), and are from the "silence" version of each test. The "nothing" files do not differ by more than a fraction of a dB.

The noise level only seems to decrease by a few dB at low vs. maximum volume, which explains why there is some audible hiss with very sensitive IEMs, even though the dynamic range is good at full volume (which would be too loud with those IEMs).

This post has been edited by stv014: May 4 2013, 12:33
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