It is possible to just turn up with recording equipment and get a great Deltic recording, as the element of luck always play a big part in success. However, if you are going to a lot of trouble and expense, and perhaps travelling some distance to the recording location, then you will want to maximise the odds of success.
Breaking the rules
The rules for good Deltic recordings may conflict with established railway recording rules. Firstly, you need to understand where the various sounds emanate from, on a Deltic loco. When idling, you hear a low frequency sound from the engines' air-intakes. These are the grills situated above each nameplate, half way along the bodysides. The engine nearest the front end, is served by the air-intake on the left-hand side.
The best idling sounds are when you can hear both air-intakes, and you will hear an accoustic effect known as "beating". This is a pulsating effect caused by two similar sounds that are at slightly different frequencies. The difference in frequencies gives the number of pulses per second heard, so you can hear a variety of rhythms depending on the engines' behaviour at that moment. With the air-intakes at opposite sides of the loco, that presents a slight problem. To hear both, you need to pick up one of the sounds reflecting off buildings or other trains, and so you need to avoid being right alongside the loco.
If the Deltic is running on only one engine, then it generally sounds best from the air-intake side, which is on the opposite side to the same engine's exhaust outlet.
For recording a Deltic pulling away from a station, it should be noted that only one engine picks up at first, and its air-intake is on the left-hand side. If you stand on the right, you will tend to hear the idling engine almost drown out the one that is revving up. This conflicts with the general recording rule about keeping well back from a train departing, which in practice usually means being to the right-hand side of it. Sticking to the left-hand side can help during other lineside recordings too, if the loco is likely to ease off (signal-checked or running slow-line), then you will still get a good sound from the one engine that is still revving.
If you are confident that it will be on full power, then it does not matter which side you record from.
The exhausts become audible when the engines rev up, creating a rasping roar. This sound varies depending on the level of silencing. Deltics returning to the main line have tended to have almost silent exhausts, although becoming louder after a few months of regular running. New exhaust lagging seems to have a major influence on this loudness, even though the lagging is on the outside of the exhaust system, and exhausts go quiet again with each lagging renewal. There is not much the sound recordist can do about this, except note which Deltics have the loudest exhausts and then chase after them while you have the chance.
The microphone should be kept inside the carriage for best results. If held outside, even the best wind protection won't prevent buffeting above about 15mph. Any make-shift wind-shield to cope with higher speeds, will probably impare the sound quality. Also, the harsh noise of the wheels is picked up from outside along with harsh reflection from the body side of the train. The mic should be just inside the open window, out of the main air-stream when the train is in motion. Sometimes, good results are obtained by having the mic right inside the vestibule, if there are no people around creating unwanted noise. This approach reduces harsh wheel noises and focuses on engines droning away. You can also arrange the mic to pick up the two engine air-intakes on opposite sides of the train, for a nice stereo effect.
The sound in the front cab tends to be less exciting than the external sounds, but if you have the driver's co-operation, sitting in the secondman's seat with the side window open, can produce a great recording, with a mix of familiar engine sounds and in-cab details. The rear cab produces the best on-train recordings, as one may be able to open all the windows without upsetting the crew, and the engine sounds drift back. As with normal on-train recordings, the mic should not be placed outside. It should be just inside the open window, positioned where it will not be buffeted by the air-stream. This is how I did some of my rear cab recordings of D9000 during its stint of Virgin service train work in 1999.
Recording in the engine room can produce particularly good results if the mic is between the two power-units for a stereo effect. The very high sound level (over 120dB) means that ear protection is mandatory, and even then, it may affect your hearing if you stay in there for long. The sound recording equipment also needs to be able to cope. My mini-disc recorder, without mic pre-amp, coped well with the record level set nice and low. Most good microphones should be able to handle the loudness without distortion. The engine room is a dangerous environment, and suitable staff supervision is certainly recommended to ensure your safety.