With the aid of a real- time FIR filtering engine or . You will need a measurement program such as Room EQ Wizard (REW) and measurement hardware such as the UMIK- 1 and a microphone stand. To effectively use this app note, you will need to be familiar with some basics of acoustic measurement, loudspeaker design and DSP. Please see the following app notes for background information: Functional overview .
While it is possible to use re. Phase to correct for room issues, it is intended to be a loudspeaker design tool. In this app note we will give an example of each of the two loudspeaker design scenarios above. The re. Phase user interface allows you to import a measurement from your measurement program and then manipulate the amplitude and phase of the correction filter.
The interface is quite intuitive and includes a graph of the predicted response and a large number of controls, many accessed via tabs: The phase and amplitude correction features are accessed from the main set of tabs: We will cover each of these tabs in the examples below. The key point in understanding how re. Phase works is that it allows you to adjust the amplitude and phase responses of the filter independently. Examine the following figure, in which amplitude is shown as the solid blue line and phase as the dotted blue line: In this figure, there are three filters applied at different frequencies, as follows: 1. Hz: a minimum- phase notch in the amplitude response. In addition to the notch in the amplitude, there is a wiggle in the phase response around the center frequency. This is typical of a normal parametric equalizer (digital IIR or analog).
Hz: a linear- phase notch in the amplitude response. Note that even though the amplitude changes, the phase is completely unchanged around the center frequency.
Hz: a phase shift generated by re. Phase, but with no change in the amplitude response. This enables re. Phase to correct or . This technique can be used regardless of whether the crossover is passive (inductors and capacitors in the loudspeaker box), an analog active crossover, or a DSP active crossover. The example speaker has a fourth- order (2.
B/octave) Linkwitz- Riley crossover at 3 k. Hz and is a sealed box with a rolloff at 8. Hz. First, we measure the loudspeaker's response and then import the measurement into re. Phase. To apply the phase correction filters in re. Phase, go to the Filters Linearizationtab and add correction filters for the crossover and for the 8.
Hz rolloff: In the figure below is the original response in red, with amplitude shown as the solid line and phase as the dotted line. The predicted response is in blue. As you can see, the amplitude is unchanged but the phase is flattened out (because phase . Here is the measured phase of the example speaker, with the phase of the uncorrected speaker in red, and the phase after the correction filter has been applied in blue: In general, a loudspeaker crossover may not always be quite so easy to linearize.
It's like a graphic equalizer, but for phase! Unlike a graphic equalizer, the Q (sharpness) and center frequency of each bell can be changed in addition to the amount of phase shift. The result from using the paragraphic phase EQ for additional phase correction at low frequencies is shown in the graph above in green. The effect of the phase correction can be observed in the time domain in various ways.
Room EQ Wizard: REW Room Measurement Tutorial Glenn Kuras. Subscribe Subscribed Unsubscribe 3,778 3K. Want to watch this again later? Sign in to add this video to a playlist. Details of the.mdat file extension; REW Measurement Data. If you don't know how to set the.mdat file association, check the FAQ.
Buy miniDSP UMIK-1 USB Measurement Calibrated Microphone: Multipurpose - Amazon.com FREE DELIVERY possible on eligible purchases. MathAudio Room EQ VST/AU and Room EQ for Foobar2000. Works with USB measurement microphones. Screenshot of the MathAudio Room EQ VST/AU plug-in. You can find what program a.MDAT file can be edited.mdat - REW Measurement Data.mdat file format description: MDAT format Application: REW Category: Data files. Many people believe that room measuring is needed to know how to. This program is offered. Click the Measure button in the upper left of the main REW screen, and you'll see the Measurement screen shown in. MiniDSP UMIK-1 USB Measurement Calibrated Microphone: Amazon.ca. If you are looking into room correction this mic plus a freeware program like room eq wizard is the cheapest way.
What is Room EQ Wizard (aka REW)? REW is room acoustics analysis software for measuring and analyzing room and loudspeaker responses, and is very handy for measuring the sub response in your room. It is free and downloadable from. Welcome to PureBits.com. To learn more about program features and specifications click here. Moreover, Sample Champion is.
For example, here are the impulse responses of the loudspeaker before (in red) and after phase correction (in blue): Here is a 2 k. Hz square wave as seen by the microphone, before phase correction: And after phase correction: Example 2: a linear- phase crossover . As an example, we re- did the above speaker with a linear- phase two- way crossover. One Open. DRC per channel can be used to implement a two- way crossover, or the mini. SHARC for up to a stereo four- way crossover. The drivers must first be measured without any crossover filters in place. You should prepare the measurements for use in re.
Phase by applying some smoothing or gating, as this will make it easier to make amplitude corrections. For each driver, you will then: Export the measurement from the measurement program (in REW, go to File!
Here's the woofer measurement of the example speaker loaded into re. Phase shown in red, and the predicted response after steps 1 to 5 above in blue: The next step is to select a crossover filter. Here is the setting used for the woofer in the example speaker, an overlapping crossover with a steep (9. B/octave) cut- off: To export the impulse response, use settings like those shown in the following screenshot. It's recommended that the . Each driver should be done in a separate re.
Phase project. The impulse responses can now be loaded into the Open. DRC or mini. SHARC and the drivers re- measured individually and then in combination. Time alignment may be needed to adjust for acoustic offsets of the drivers and differences in the location of the impulse response peak. The following graph shows the measured amplitude responses of the example speaker, where the individual responses of the woofer and tweeter are shown in blue and green, and the combined response in mauve (see notes 5 and 6 below). This is the measured phase response of the example speaker: Usage notes . Here are some additional notes on usage: While you can put in almost anything you like for the correction or crossover filters, the requested filter may not be realizable depending on the length of FIR available.
After pressing Generate, re. Phase will show the actual response that can be achieved in red. The generated FIR filters are not causal — that is, the impulse response starts . For stereo audio playback, this is usually not a problem, but it may be a problem when synchronization with video is needed (home theater), for music recording or in live performance.
The part of the FIR impulse response before the peak is sometimes referred to as . If the FIR filters for each driver are of different lengths, then time delay will be needed to re- align the acoustic signals from the drivers. Any digital filter or speaker design program is a tool to aid you in creating a good speaker, but driver selection and cabinet design are also very important. For example, the measurements above show an issue in the 7- 8 k. Hz region that should not be . Rather, an investigation is needed into a better design of the cabinet and/or a different tweeter.
The on- axis measured response is, of course, taken at only one point in space. Because a loudspeaker uses multiple drivers, there will be interaction between them so that the response will be different at other points in space. The off- axis responses, both horizontally and vertically, should also be measured and optimized to meet your design goals.
If re. Phase is not the most suitable for your FIR filtering project, please see these other app notes for more options.