Tapiir 0.7.1 review
DownloadTapiir is a simple and flexible audio effects processor, inspired on the classical magnetic tape delay systems used since the early d
|
|
Tapiir is a simple and flexible audio effects processor, inspired on the classical magnetic tape delay systems used since the early days of electro-acoustic music composition.
Tapiir project provides a graphical user interface consisting of six delay lines, or "taps", which can introduce an almost arbitrarily big or small delay to their inputs and can be feed back to each other.
A wide set of effects can be easily achieved by properly configuring and connecting the delay lines: complex echo patterns, resonances, filtering, etc. Delays, interconnections and gains can all be controlled in real time.
TAPIIR internal processing modules consist of six delay-lines, each with a mixer at it's input and a gain control at it's output, and a stereo output mixer. Stereo input from an external source, typically a musical instrument, is routed to all input mixers. In addition to this, the output of each delay line is also routed to the input mixers of all delay lines, including itself. Figure 1 shows the diagram of TAPIIR's internals.
This cross-feeding of audio signals throughout the system of delay-lines and mixers, allows the user to create a very large variety of stereo delay effects. Very simple echos or ping-pong effects can be achieved easily, but more complex effects such as early reflection echo's, reverbs, complex rhythmic and arrhythmic patterns and even Karplus-Strong like synthesis is also possible. It is important to observe, that these more complex effects are only possible by using sample accurate processing.
This article appears in Proceedings of the COST G-6 Conference on Digital Audio Effects (DAFX-01), Limerick, Ireland, December 6-8, 2001
Sample accuracy
Conventional hardware effect processors are often rather limited in the lenght of there delay-lines. It is unusual to encounter accuracy higher than 1 msec, and even 10 msec is used frequently, and maximum delay-lenght are limited as well.
Obviously, this limitation in hardware effect processors is deliberate, both out of technical concerns or marketing. Most users are not interested in higher accuracy, and the standard user interface of hardware effects processors - buttons or at the most an alpha-dial - would make it a painful job to adjust. Also, one can imagine that lower accuracy means less computational cost, and therefore lower overall cost of the effect processing hardware.
For advanced users however, this limitation can be annoying. Of course, many of the effects obtained with very short delay times, such as reverb or filtering, are usually also implemented in the same hardware, but it can be very interesting to combine all these with longer delay-time effects; it would be necessary to use several processors connected together to do this.
The implementation of TAPIIR, however, is sample accurate. This means that extremely short delay times can be used, 0.023 msec when using a sample-rate of 44100 Hz. In addition to this fine control over delay-lengths, the sample accuracy is also implented for feedback and even cross-feeding between the various delay-lines, This is achieved by the fact that the internal processing core of TAPIIR is written in such a way, that the input and output values of the delay-lines and mixers are passed on 1 at a time, instead of buffer-by-buffer.
Filtering with delays
Obviously, the effects obtained by sample accurate processing of delay-lines go far beyond the simple echo effects. This includes the creation of FIR filters and - using feedback - IIR filters (this has been the inspiration for the name TAPIIR). In these cases, the mixer gains function as filter coefficients. This means that TAPIIR can efficiently be used for filtering, with flexible filter design. In a future version, TAPIIR could contain a pole/zero editor that automatically sets the mixer values to create the corresponding filter.
The maximum delay-length that can be achieved is only limited by the physical RAM memory of the system TAPIIR runs on. To give an example, with 32 MB of free memory, a total delay-length of more than 6 minutes can be used. While this might seem rather useless for normal effect processing, it clearly has musical applications. Several compositions have been written that make use of long delay times. Originally performed with the use of tape-delays, they could take great profit of the use of digital techniques for sound quality. The use of hard disk space with sufficient fast access would take away time limitation even more.
Delay-length control
The graphical user interface of TAPIIR allows the user to take full advantage of the delay-length accuracy, but at the same time it tries to maintain user-friendly and manageable, by offering value-sliders for larger scales as well. Delay-time can be entered in time in seconds in number of samples. Sliders control the digits of the delay-length, with an accuracy of 5 decimals. An additional feature is the use of tempo/signature. In that case, delay-length in not represented in seconds, but in beats, and the sliders control the subdivision of beats according to the signature. Obviously, in many circumstances this representation is a lot more useful, in a musical sense, than time in seconds.
Requirements:
ALSA sound driver (0.9)
Tapiir 0.7.1 search tags