Whether you are sampling a bedroom or a digital reverb unit, whether you use a portable radio or Pro Tools connected to a PA system, the basic steps are always the same:
This video shows everything involved in making an impulse response of a church.
The files here are 48 kHz interleaved 24 bits stereo wave files that have proven to transfer well to many hardware players. The sweep is in the Left channel of the file. If you want to record using a DAW, just split the stereo files and use only the sweep channel.
On a busy film set when people are waiting, time is limited. When you do not have the time to use an entire minute per take use one of shorter sweeps below. Do select the proper sweep for the length of the reverb you wish to sample. The major disadvantage of a shorter sweep is that there will be more noise in the IR. If possible use the 30 seconds sweep, when time is limited use one of these short (fast) ones.
|1s sweep for 10s reverb||44.1k||48k||88.2k||96k|
|1s sweep for 28s reverb||44.1k||48k||88.2k||96k|
|3s sweep for 1s reverb||44.1k||48k||88.2k||96k|
|3s sweep for 3s reverb||44.1k||48k||88.2k||96k|
|6s sweep for 3s reverb||44.1k||48k||88.2k||96k|
|10s sweep for 3s reverb||44.1k||48k||88.2k||96k|
|10s sweep for 7s reverb||44.1k||48k||88.2k||96k|
|10s sweep for 15s reverb||44.1k||48k||88.2k||96k|
|10s sweep for 42s reverb||44.1k||48k||88.2k||96k|
|30s sweep for 3s reverb||44.1k||48k||88.2k||96k|
|30s sweep for 8s reverb||44.1k||48k||88.2k||96k|
|30s sweep for 16s reverb recommended||44.1k||48k||88.2k||96k|
|30s sweep for 45s reverb||44.1k||48k||88.2k||96k|
|100s sweep for 3s reverb||44.1k||48k||88.2k||96k|
|100s sweep for 16s reverb||44.1k||48k||88.2k||96k|
|100s sweep for 45s reverb||44.1k||48k||88.2k||96k|
Spring reverbs, echo chambers, plate reverbs and other analog reverbs: please use the sine sweep files under Sampling Acoustic Spaces.
Digitally connected reverb gear: use the spike file. The spike is preferred when capturing presets with time variant features like chorus or wander.
The DA and AD conversion will cripple the spike when sampling an analogue unit and this will affect (badly) the timing in the IR. Better is to use a short sine sweep then. Under more sweeps you can find a 1 second sweep that will do just fine.
Several types of audio can be dropped onto Altiverb and made into Impulse Responses. All of them require you to drop the recording onto the IR import tab of Altiverb. The movie at the top shows how to switch to the IR import tab, and how to bring up the dropped audio description popup menu, of which we discuss the options one by one.
Select this if the audio you are dropping is a finished impulse response (downloaded from somewhere, or obtained using a digital spike recording through effect gear) , or if you want to experiment using other audio. Special effects can be achieved by using audio such as piano chords, breaking glass, spoken word, or drum rhythms. Select this item, drop the audio and listen to the result. Whenever you like an impulse response do not forget to save it using the save to User IR folder button. Using audio like piano or voice normally results in material that sounds too dull. You need to really boost high frequencies. This is what the turning knob is for. It is a special type EQ called Enhance. What happens when you use a piano chord as an IR and then sing through Altiverb, is much like what happens when, in lighting, you want to use a blue and a red translucent filter to create a purple one. It does become purple, but it also becomes rather dark. In audio, the piano has a ‘pink’ distribution of frequencies. Pink means the high frequencies roll off at a certain very natural rate. The voice is ‘pink’ as well. Convolute them, which is a multiplication in the frequency domain, and you will see the roll-off slope is twice as steep. Very unnatural. To make up for that you can use the enhance knob which is a pink-to-white EQ and can bring back the high frequencies.
Download sound files that contain a sweep tone from this page. These are meant to be played back in a room of which you want to capture the reverb in an impulse response. Microphones should be used to record the playing back of the sweep tone in the room. The resulting recording can be dropped onto Altiverb. When this quality speaker option is selected The sweep tone will be calculated out of the recording and you will hear the resulting reverb right away. Altiverb will assume that you have used a quality speaker to play back the audio and will not attempt to make up for any frequency deficiencies of the speaker. There are many advantages of using the audio ease method of creating impulse responses. The sweep is not equal loudness throughout, its level is higher where most speakers can take it and where the ear is more sensitive, resulting in less noise. The Altiverb sweep method is immune to clock differences between playback and recording gear. Altiverb is unique in this respect. You can safely use one recorder to play back the sweep and another to record. You can playback and record at vastly or slightly differing samplerates, it is all no problem to Altiverb. Third and fifth harmonic distortion, happening in a speaker that gets overloaded, sounds like a reflection of the sweep that started earlier than the sweep itself. In the result that will be cut off and will not affect the result. All reverb tails eventually dive into noise. At that point Altiverb needs to figure out how to fade out the tail. Audio Ease’s extensive experience has resulted in the best fading algorithms, carefully taking into account the exact shape and onset of both reverb and noise. Many of the ground breaking technology improvements that have led to the quality of the Altiverb IR library are available to you, in Altiverb’s 7 drag and drop sweep method.
You play back a sweep much like described under quality speaker, but this time through a Tivoli PAL portable battery powered radio. The Tivoli PAL radio is small, surprisingly wide-band, portable, available for over a decade now, and you can plug your iPod or other playback device right into its back. For making quick Impulse responses intended for treating voices it can be ideal. However, the EQ curve of the Tivoli speaker goes up and down like nothing else, so to iron that out, choose this option.
If you need to match audio from a film set and the only thing you can find to make an impulse response from is the slate clap, you can cut it out drop it onto Altiverb and make an IR out of it.
Audio Ease has sampled the characteristics of the two most common slates (clapper boards). The Denecke and the Ambient. If the results come out too noisy you can use Altiverb’s similar function (from the IR Browser) to suggest impulse responses from the Altiverb IR library that match the acoustics from the film set.
A six millimeter caliber Flobert starter pistol can be used to make impulse responses. Use hearing protection when you use these and do not try to carry a starter pistol into a public space without telling everybody first. Because a starter pistol is loud the resulting signal to noise ratio is second only to the sweep method.