Taking bell recordings - part two

[oakcroft13]

Here are some further ideas (born in the main of bitter experience) 
concerning the recording of bells. The issues I'll address here 
include:
* frequency stability of recorders
* automatic level control
* frequency response of microphones and speakers
* the loudness of bells
* ambient noise and recording location.

1) Frequency stability of recorders
If you are recording bells for analysis purposes, or just want the 
pitch to be accurate, frequency stability (i.e. variations in record 
and playback speed) can be a real problem. Some guidelines are:
* domestic cassette recorders are usually terrible in this respect
* where possible, play back recordings on the recorder they were 
taken on (though this is often not enough to fix the problem)
* speed variations can be compensated for by recording tuning forks, 
handbells etc. but this is a real fag to do
* machines I have used that display good stability include video-
cameras and recording direct to PCs. Steve Ivin and George Dawson 
speak highly of mini-cassette recorders, I have no personal 
experience.

2) Automatic level control
This is an unfortunate feature of domestic cassette recorders and 
other such beasts. Because bells are so loud compared with ambient 
noise, recordings with auto level control usually consist of a loud 
hissing noise interrupted by the fainter sound of the bell or bells. 
If the level control cannot be over-ridden you will not get good 
results. Video cameras (based on the small sample of those I have 
owned) appear not to have auto level control and are OK.

3) Frequency response of microphones and speakers
Speaking subjectively (because I have not done detailed response 
tests, yet), even quite small, cheap microphones give good frequency 
response and dynamic range. Video camera microphones have proved 
good, and the microphone I use with my laptop came (ahem!) free with 
a PC I bought a few years ago. On the other hand, cheap and small 
loudpeakers are usually very poor, with bad bass response and fake 
resonances. You need to play recordings back through hi-fi equipment 
(or at least PC speakers that cost more than £15!) to judge their 
quality.

4) Loudness of bells
Bells are very loud indeed, as we all know. I have found that a 
single clapper blow recorded close by the bell will easily overload 
the various recorders I use. There are two ways to get around this. 
First, distance always helps - recording from another floor, further 
from the tower etc. Learn the characteristics of your recorder and 
how close you can get without overload. Just because the recording is 
not audibly distorted does not mean that you are free of overload - 
looking at the file with a sound-file editor will tell you if 
clipping is occurring. Aim for no more than 80 or 90% of full scale 
to be sure. The second cure is to always do a level check before 
taking a final recording, and either move further away or turn down 
the record level to get satisfactory results. Aim low - within 
reason, loudness can be boosted with a sound file editor but there is 
no way to remove overload.

5) Ambient noise and recording location
The ability of recorders to pick up blackbirds, traffic, wind and 
bellropes is remarkable. Wind can to some extent be cured with a hood 
on the microphone (I believe, I have not tried this). The background 
noise needs to be minimal for a good recording. In achieving this, 
watch for multiple sound paths from the bells to the microphone. 
Examples include: echoes off surrounding buildings, closeness to a 
bell-opening, or to a hole in a floor giving undue prominence to 
certain bells, etc. Locations inside the tower are often 
satisfactory, especially if it is possible to go above the bells with 
an intervening floor or two to cut the volume down. On floors below 
the bells, rope or mechanical noise often spoils the recording. If it 
is sheltered from the wind, the roof of the tower may be a good 
location. The church roof is often too close to the bell openings on 
one side of the tower. Some of the very best recordings I have heard 
were taken in the bell chamber, but needed professional equipment 
capable of handling the sound intensity.

Hope the above thoughts are useful. They are not definitive, I'm sure 
others have views.

Bill H