Measuring Loudspeaker Impedance with IOScope

Today, a new video, Measuring Loudspeaker Impedance with IOScope, was published on this site, as well as on the Faber Acoustical YouTube channel. The video is both a demonstration of IOScope, as well as a simple tutorial on measuring loudspeaker impedance. Although the video is largely self-explanatory, I thought it would be beneficial to include some further explanation and tips for those who are interested. The movie is essentially broken into four chapters and a similar format will be followed here. What is impedance? How is it measured? By a generalized version of Ohm’s law, we understand that voltage is equal to the product of electrical current and impedance. This means that electrical impedance is equal to the ratio of […]

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iPhone Microphone Frequency Response Comparison

With the advent of sound level meter apps for the iPhone OS (of which SoundMeter was the first) people began to ask, “How flat is the frequency response of the iPhone’s microphone?” Early testing indicated that the built-in microphone of the original iPhone was not a good candidate for sound level measurements, but that the iPhone’s headset microphone enjoyed a fairly flat response. Since then, additional iPhone models have arrived on the scene, each with its own set of weaknesses with respect to microphone frequency response. Additional Apple and third party headset microphones have also been introduced. At long last, some relevant frequency response measurements are presented here for the benefit of those who would really like to “see” how […]

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iPhone Line Input Frequency Response Comparison

Although I already listed some options for getting line-level audio into an iPhone or iPod touch, that list didn’t include much information that would suggest which option would be best. One important metric that people frequency ask about is frequency response. Well, I finally have some frequency response comparisons available to help answer that question. These measurements were made of various dock connector devices, attached to an iPhone 3GS. As in other frequency response measurements, the audio was routed through the iPhone, with a little help from SignalScope Pro. This means that each measurement includes the frequency response of the iPhone 3GS headphone output. The tested devices include: Tunewear Stereo Sound Recorder for iPod Alesis ProTrack Griffin iTalk Pro MacAlly […]

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iPhone Dock and Headset IO Frequency Response

People often ask about the frequency response of iPhone and iPod touch audio inputs. To shed some light on the issue, I made some frequency response measurements of the iPhone, iPhone 3G, iPhone 3GS, and iPod touch 2G with Electroacoustics Toolbox and an Edirol FA-101 audio interface. These measurements are broken into two groups, one for headset input and one for dock connector input. Since measurements were made by routing audio through each iPhone OS device (by way of the Audio Play Through function built-in to SignalScope/Pro), all measurements include the frequency response of the headphone output in addition to the response of the selected input. The frequency response of the Edirol FA-101 was removed from the measurement, using a […]

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Measuring Time Delay with Electroacoustics Toolbox

Measuring Time Delay in an Audio System Using Electroacoustics Toolbox Although Electroacoustics Toolbox is not limited to measuring audio systems, the measurement of audio systems is a common use that offers convenient ways to demonstrate the capabilities of the software. These examples can then be applied to other applications in which the Toolbox’s measurement capabilities may be considered useful. At times it is desirable to measure the delay of a signal through some component, or group of components, in an audio system. For example, when a digital signal processor (DSP) is employed in an audio system, to optimize or otherwise alter the listening experience, it may be desirable to measure the delay introduced by the DSP’s algorithms in the audio […]

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Measuring Audio Unit Effect Plug-ins With Electroacoustics Toolbox

Measuring Audio Unit Effects Plug-ins Using Electroacoustics Toolbox, Soundflower, and AU Lab A valuable use of Electroacoustics Toolbox is measuring Audio Unit effects. Measuring Audio Units can be useful to developers of such plug-ins, or to anyone employing Audio Unit effects in their digital audio recording, editing, or reproduction system. This tutorial requires two free software packages in addition to the Toolbox: Soundflower and AU Lab. AU Lab is distributed with Tiger (Mac OS X, 10.4). Soundflower is a free system extension for Mac OS X, version 10.2 or later, that allows for convenient routing of audio signals between applications on the Mac. More information regarding Soundflower, as well as a download link may be found at cycling74.com. (Version 1.2 […]

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Audio Interface Frequency Response Measurement with Electroacoustics Toolbox

This article was originally published in the forums for version 2 of Electroacoustics Toolbox. Please visit the following link for an updated tutorial for version 3. Frequency Response Measurement with Electroacoustics Toolbox 3 Measuring the Frequency Response of Your Audio Device One of the most powerful tools in Electroacoustics Toolbox is the Dual FFT Analyzer, which is capable of measuring system transfer functions and even indicating the quality of the measurement. This tutorial focuses on using the Dual FFT Analyzer to measure the frequency response of the audio device that you use to measure other systems and devices. If you want to measure the frequency response, or impulse response, of a listening room for example, that measurement will be affected […]

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iPhone Headset Input Options

One of the most obvious ways to get analog signals into an iPhone or 2nd generation iPod touch is through the headset connector. Several options exist for getting acoustic or electric signals into the headset input, which are discussed below. Any of these options will work with the iPhone, iPhone 3G, or iPod touch 2G. The original iPod touch does not have a headset connector with a mic input channel, so it is left out of this discussion. When making a decision about what to use the headset input for, or what to connect to it, you may want to take a look at the frequency response measurements of the various iPhone OS devices. Acoustic Signals Acquiring acoustic signals requires […]

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Dock Connector Audio I/O

Several options exist for getting audio signal into and out of iPhone OS devices via the dock connector. However, not all accessories are compatible with all iPhone OS devices. So, we put together this compatibility chart, based on our own tests with SignalScope/Pro and SignalSuite. Dock Audio Accessory Compatibility These devices were chosen for their ability to accept stereo audio input from external sources. Some dock connector devices simply feature built-in microphones, which are of limited use for test and measurement applications. It’s also important to remember that the iPhone OS automatically selects the current route for input audio signals (built-in mic, headset, dock connector, etc). iPhone iPhone 3G iPod touch iPod touch 2G Alesis ProTrack In/Out(1,2) In/Out(2) Out(3) In/Out(2) […]

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