Harmonic distortions of the unbalanced inputs
Edirol R-4, Zoom H4n, Sony PCM-D50
Ok, so there is not a big difference between the units when it comes to noise level. But what about harmonic distortions?
I connected the unbalanced 1/4" TRS (tip-ring-sleeve) line-inputs of the Zoom H4n and the Edirol R-4 to a pretty good Marantz CD-player and played back a test-CD with a pure 1 kHz sine-wave.
You might argue that the analog circuitry of the CD-player would introduce some harmonics as well, and that is probably correct. But the results of the Edirol proved that this wasn't much.
Before the recording, I reduced the output of the CD-player so that the Zoom at an input-level setting of 1 (the lowest setting) would just not trip. This was equivalent to a setting of Line-5 with the Edirol. Obviously, the Edirol has some reserves for even hotter signals while the Zoom is at its limit. The test with the Sony PCM-D50 was done later at full output level of the CD-player. The Sony's record level had to be set to 4.5 to maintain about -1 dBFS. Again, plenty of reserves for hot line signals.
All tests were done on battery power to make sure no distortion could creep in from an AC supply.
1 kHz, -0.5 dbFS sine wave on an Edirol R-4
The spectrum shows a first harmonics (k2) of 2 kHz at a level of -100 dB. Since the base frequency (k1) would peak at -10 dB this computes to a harmonic distortion of -90 dB, which is excellent. The second harmonics (k3) at 3 kHz is even lower.
It seems my CD-player isn't too bad after all ;-) You can download the wav-file of the Edirol's recording here.
I have also checked the noise level of this setting (Line-5) when the CD-player was off and it was -80 dBFS. Again a very good result.
1 kHz, -0.5 dBFS sine wave on a Sony PCM-D50
The Sony performs even better than the Edirol though the difference is marginal. The k2 harmonics is practically the same (-90 dB) but there are not further harmonics exceeding -100 dB.
1 kHz, -0.5 dBFS sine wave on a Zoom H4n (record-level 1)
Obviously the Zoom H4n doesn't like hot signals so I checked different record-level settings (always adjusting the output of my CD-player to a constant -0.5 dBFS) - see the table on the right.
k2 and k3 are given in dBFS relative to the fundamental tone and as a percentage. The total harmonic distortion factor (THD) is the geometric sum of all the individual distortion factors. The first table row, for example, computes to a THD of about 0.7% (k4 and higher harmonics are small enough to be disregarded in this case).
The links take you to wav-files of the Zoom's recordings. Each is about 8-10 secs in length.
I did tests with even higher record-levels than 50 but the higher I got the more I had to reduce the output of my CD-player - and that would add extra harmonics. Even the last values of the table should be taken with a grain of salt.
1 kHz, -0.5 dBFS sine wave on a Zoom H4n (record-level 40)
We are slowly getting there... Raising the record-level will improve the results somewhat. But that is only a practical solution if your input signal can be turned down enough or you have a attenuator pad at hand because the Zoom doesn't have one built in.
I have done many more tests and found that this game also works the other way around.
You will get acceptable distortion at the lowest record level (1) as long as you input signal is kept below -12 dBFS. For a record level of 10, the input signal should not exceed -9 dBFS and so on.
For me, acceptable means k2 and k3 between -60 and -70 dBFS relative to the fundamental frequency.
But 1kHz is not all. Let's now look at a 10 kHz test tone:
10 kHz, -0.5 dBFS sine wave on the Edirol R-4 (line-8 with 18 dB pad)
Great result. k2 is at -85 dBFS relative to the fundamental frequency. Download the wave here.
10 kHz, -0.5 dBFS sine wave on the Sony PCM-D50 (rec-level 4.5)
The same great result as the Edirol. The k2 harmonics is even a tad lower. But at a level of -85 dBFS there is really nothing to worry about (after all, I am not using a professional signal generator and this peak may well come from my CD-player anyway...).
Now on to the same test with the Zoom H4n:
10 kHz, -0.5 dBFS sine wave on the Zoom H4n (rec-level 40 with 18 dB pad)
Some final remarks on the Zoom H4n (added 2012/01/07)
Recordings through the unbalanced inputs should never be made anywhere near the max. rating (+2dBm) or otherwise they will be distorted (THD of up to 1%).
A "REC LEVEL" setting of 50 or higher will give acceptable results (THD below 0.1%) provided the signal is muted enough not to overload the inputs.
I did not test the balanced inputs as I did not have the proper equipment to do so.
More "final" remarks (added 2012/02/20)
I have been in contact with an audio engineer recently who did some pretty thorough testing on the balanced and unbalanced inputs of the H4n. He also conducted an acoustic test using an Agilent/HP audio oscillator at 10 kHz, audio amp and tweeter directed at the H4n's built-in microphones. Not only did he confirm my findings but he also found something very disappointing about the microphones:
The balanced inputs are free of distortions but the microphones exhibit the same distortions as the unbalanced inputs.
To quote from his analysis of the Zoom H4N "All very interesting but shamefully poor design. I would call this a voice grade unit for non critical use at best."
The engineer opened his H4n to follow the signal path of the microphone signals. He was able to verify that the built-in microphones are using the same signal path as the unbalanced inputs and are subject to the same distortions with respect to the input level control setting. He points out the distortions mostly affect the high frequencies > 5 kHz and only at very high input levels. He does not recommend this recorder's microphones for very serious applications. It is not a professional level product. He also noticed that the balanced inputs are somewhat high level. They lack sufficient gain for using dynamic microphones without an additional mixer or preamp.
I also came across a very interesting Microphone Input Noise Comparison.
Not surprisingly the H4n ranks in the low end of all the handheld recorders tested.