I use a Sennheiser MKE300 external unbalanced mic, which costs about £150 these days, so not cheap but not in the same league as a "proper" balanced mic. The pick-up pattern is somewhere between hyper-cardioid and short-shotgun. The low frequency response is not too special but that helps the off-axis rejection, since bass frequencies are the least directional, and also reduces the wind noise for outdoor use. I used it in a shock mount on my old XM1 (auto level only) for many years to good effect, and now I'm using it on my XH-A1, also with auto-level switched on.

I have recently had a problem with distortion that I never had on the XM1. I was videoing a steam train recently (I do that a lot!) and found that a loud blast on a chime whistle was horribly distorted. I was stood about 50 - 100 yards from the track as the loco passed. I'm sure that I've recorded the same locomotive (LNER A4 class pacific no 60009, for those interested in such things), when stood rather closer, on previous occasions on the XM1 and not had this problem. I reckon that either the unbalanced input on the XH-A1 doesn't match the MKE300 as well as the XM1 did, or the XH-A1 preamp distorts at a lower signal level, or a combination of both. I don't think it's the AGC because the distortion carries on for as long as the whistle sounds. If the AGC was just slow to react, then I'd get distortion at the beginning of the sound but it would reduce as the level came down.

The specs that I can find on the web for the MKE300 are:
Frequency Response 150 Hz - 17 kHz, (-3 dB)
Dynamic Range (Typical) 98 dB
Signal-to-Noise Ratio 76 dB
Maximum Input Sound Level 116 dB, (THD = 1 %)
Output Impedance 200 Ohms
Sensitivity (free field, no load, 1 kHz): 16 mV/Pa ± 2.5 dB <<== is this the important one?
Equivalent noise level
-- A-weighted (DIN IEC 651): 18 dB,
-- CCIR-weighted (CCIR 468-3): 28 dB

I have looked in the XH-A1 manual (PDF from the Canon web site), but the only specs that I can find for the unbalanced audio input are these:
Type of plug: 3.5mm dia
Input impedance 600 ohms
Sensitivity 64 dBV (automatic noise level setting)

Can someone who understands these things give me an idea of how well matched the MKE300 is to this input? Are the impedances in the right ball park? How should one convert Sensitivity from mV/Pa to dBV?

A friend uses the same type of mic on his Sony FX1, and I have noticed that his audio levels are much lower overall. He's also using auto level and not using the MIC ATT switch, so I guess that the Sony unbalanced socket/pre-amp is less sensitive than Canon's.

The -20dB MIC ATT option is a bit drastic for normal use, and the +12 dB boost (to give a theoretical -8 dB cut) only works on the XLR channels, not the unbalanced socket, assuming I've read the manual correctly. Maybe I need an external "pad" between the mic and the socket? -5dB? -8dB? Does anyone make a (stereo) unbalanced mini-jack pad that's compact enough? Any suggestions?

I'm intending to upgrade to a "proper" mic before too long, but that's a bigger decision involving A/B tests of various different mics, shock mounts and wind mufflers, which take a while to organise. Right now, I'm looking for something to tide me over for the next few months.

If you are connecting top the 3.5 mm phone plug mic jack, be sure to activate the MIC ATT setting for that jack (on the top under the LCD panel). it will give 12 dB attenuation, and should go a long way to solve distortion problems at the mic input jack due to excessive input levels (And be sure that the mic input sensitivity from the menu is set to "Normal," not "High.")

The 16 mV/Pa rating of the MKE300 is a standard mic rating and corresponds to about -36 dBV output level, a fairly hot mic. This is an open circuit rating, and output will drop by about 2.5 dB as the mic is loaded by the preamp. BTW 1 Pa corrsponds to 94 dB sound pressure level. The mic may be a bit hot for recording loud sounds.

The 116 dB max sound pressure level for 1% distortion is not very loud as loud program material goes. A rock concert is more like 120 dB close in to the stage. And actual performance gets worse because even though the output impedance is 200 ohms, when loaded the actual output capability drops somewhat due to limitations on the output current capability of the mic. How much it drops depends on the internals of the mic, but it may be by as much as 3 to 6 dB SPL.

The A1 input impedance is 600 ohms, an industry standard dating back many years, but many "budget mics" are spec'ed with a higher load impedance, perhaps 1000 to 2000 ohms, as is common on many XLR preamp inputs these days.

For recording loud thing things like trains, consider a different mic, one that can cope with very loud sounds. A dynamic mic like the Shure SM57 (or SM58) might be a reasonable economical general use choice here rather than a condensor mic.

Thanks Don. Are you sure that the MIC ATT for the unbalanced mic socket on the XH-A1 is -12dB? On page 49 of the manual it says
If the audio level is too high and the sound sounds distorted, activate the microphone attenuator (12 dB with the internal microphone, 20 dB with an external microphone) by setting the MIC ATT switch (built-in microphone/external microphone connected to the MIC terminal) or the XLR MIC ATT switch (external microphone connected to the XLR terminal) to ATT".
I read that to mean that any external mic, whether attached to the MIC socket or an XLR socket is attenuated by 20 dB. So is it just the XLR sockets where the MIC ATT is -20 dB? 12 dB would be more useful in my situation. It is certainly worth some experiments...

I have a couple of SM58s that I use with my band on stage. Around stationary locos and for general ambience in a noisy location they may be just the job, but for recording passing trains in the landscape I prefer something more directional and with greater "reach". They'd also be hard to mount on the camera.

Time to have a listen to some short shotgun mics. My short list at the moment is:
Rode NTG2
Audio Technica AT897
Sennheiser K6 + ME66
Have I missed any obvious alternatives? I don't think my budget will stretch to an MK416...

On closer reading I think you are right, 20dB for external mics at XLR or 3.5 mm jacks, and 12 dB for internal mic, and that is consistent with the earlier Canon MiniDV models.

If camcorder is on a tripod, maybe put the SM58 on a stand? The cardoid pattern should be fine for the train (180 degree sound field) and will give better back rejection than a hypercardoid shotgun that usually has lobes immediately to the rear. Further, the shotguns may tend to color the sound more due to differing pickup patters at different frequencies. This may be good or bad depending you your taste.

Your short list hits the most popular models among the posts I read. The obvious alternatives include some mics from Azden (but I have some reservations about Azden quality compared to the three you listed), Sony, Shure, Bayerdynamic, Roland, etc.

I did a few experiments this weekend down at the Watercress Line (http://www.watercressline.co.uk/), and I think I my problem was the ID-10-T user-interface ;-). I think the Audio Auto/Manual switch was knocked to Manual in the bag and I hadn't noticed. I repeated some very similar shots to the ones that caused me problems, with auto-level switched on, and the high levels were adjusted perfectly with no hint of over-load.

Anyway, I've arranged to take the camera to a music & audio shop in Southampton next Saturday, to compare the microphones I mentioned last week. (They are the only one reasonably close that stock all three mics.) I'll let you know what I think when I've had a chance to listen to the results.