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Russell McClellan
In the last few years, a number of different countries have passed laws regulating the loudness of audio in television and other broadcast mediums. Surprisingly, loudness is a difficult concept to capture with a simple technical specification. Current regulations set limits for a number of different audio metrics, including overall loudness, maximum short-term loudness, and the true peak level of a signal.
What are true peaks?
To understand how true peaks differ from sample peaks, we have to go back to the basis of digital audio: the Sampling Theorem. This theorem states that for every sampled digital signal, there is only one correct way of reconstructing a band-limited analog signal into a digital one such that the analog signal passes through each digital sample. Digital-to-analog converters try to approximate this correct analog waveform as closely as possible. For more details on this fascinating theorem, we recommend this video from xiph.org.
Nov 27, 2018 Get the software used in this video here - iZotope RX. ? Adobe Audition Presets! ? The audio presets I use.
- Jul 15, 2019 Standard sample rate: 44.1 kHz. The most common sample rate you’ll see is 44.1 kHz, or 44,100 samples per second. This is the standard for most consumer audio, used for formats like CDs. This is not an arbitrary number. Humans can hear frequencies between 20 Hz and 20 kHz.
- Resample allows you to convert an audio file from one sampling rate to another. Sample Rate Conversion (SRC) is a necessary process when converting material from one sampling rate (such as studio-quality 96 kHz or 192 kHz) to another rate (such as 44.1 kHz for CD or 48 kHz for video).
- In fact, both SRC and dithering can increase peak levels of the file and cause clipping. Dither is relatively harmless: even with noise shaping, the level of 16-bit dither is usually below −60 dB. It means that it adds less than 0.01 dB to the peak level of your full-scale signal.
Some audio editors are able to display the digital samples and an approximation of the corresponding analog waveform. In iZotope RX, both of these signals appear when you zoom far enough in. The blue line represents the analog signal, while the white squares are the digital samples.
In RX, you can click and drag on an individual sample to change it and see how the analog signal reacts. For example, if you move a single sample very far, we can see that a large amount of ripple appears in the analog signal around that sample.
It’s clear that the analog signal’s peak is quite a bit higher than the highest digital sample. The highest point the analog signal reaches is called the true peak while the highest digital sample is called the sample peak. Since a digital signal has to be converted to an analog signal to be heard, the true peak is a much more sensible metric for the peak level of a waveform.
It turns out that for real audio signals, quite often the true peak is significantly higher than the sample peak, so it’s important to measure carefully.
How are true peaks detected?
BS.1770, the international standards document used as the base for regional loudness specifications, gives a suggested algorithm to detect the true peak level of a digital signal. This algorithm is a relatively simple one: first, upsample the signal to four times its original sampling rate, and then take the digital peak of the new, upsampled signal. We can perform this algorithm manually in RX: first, open the “Resample” module and select a sample rate four times the original rate, then open the waveform statistics window and check the sample peak level. Here’s what the test signal above looks like after it has been upsampled to four times its original rate:
As you can see, after upsampling, the true peak level is now very close to the sample peak.
Of course, the RX waveform statistics window already provides the true peak level, so you don’t have to perform these steps by hand.
While this algorithm is quite good, there are two major ways that errors can occur. First, no upsampling algorithm can ever be perfect, so either overshoots or undershoots can occur during the upsampling process. This problem can be helped by using a high-quality upsampling algorithm. Second, the true peak may still be between samples even after the upsampling happens. This problem can be ameliorated by upsampling at a higher ratio.
How can we measure the quality of a true peak meter?
While most true peak meters follow the same basic algorithm as the one described in BS.1770, they can vary significantly in two dimensions: the quality of the upsampling algorithm, and also in the ratio of upsampling. BS.1770 includes a description of a simple upsampling algorithm, but many true peak meters actually perform more accurate upsampling than required by the specification. Also, many meters upsample by more than the required four times. This means that true peak meters can vary significantly in the accuracy of their output.
How can the quality of a meter be measured? One way is to create a synthetic signal that is difficult to meter accurately, but has a mathematically known true peak. This way, we can compare the meter’s reported true peak to the true peak we calculated ahead of time, and any difference can be attributed to meter error.
Testing meters with single impulses
One simple signal with a known true peak is a digital impulse, a signal with all samples at zero except for a single sample at a non-zero value. We can see the analog waveform this creates by looking at it in RX:
It turns out that the analog waveform for a digital impulse is a well studied function called the sinc function and has a simple mathematical expression: . Also, the true peak is the same as the sample peak at . This isn’t an incredibly useful signal for testing true peak meters, since even a bad true peak meter that only looks at the sample peak without upsampling will get the correct answer.
However, knowing the mathematical expression for the analog signal allows us to shift it in time to create a more interesting signal. Consider a signal the same function with a time offset of a fraction of a sample, say , i.e., . This signal should still have a true peak of , since time shifting an analog signal will not change its analog peak. However, the sample peak will be lower, since the true peak no longer sits exactly on a digital sample.
We can use Python, NumPy, and scikits.audiolab to create a wave file with this shifted sinc signal:
Izotope Rx Sample Rate Chart
Then, we can open it in RX to see the digital samples and analog waveform:
As we can see, the analog waveform is the same, only shifted in time. However, now the sample peak is a few decibels lower than the true peak. We set , so the true peak is or dB. The sample peak is the sample immediately before the true peak, which using our formula above is or around dB, a difference of over two decibels from the true peak!
Since we know the exact true peak level of this signal, we can use it as a test of a true peak meter. It’s fairly difficult to measure, because a sinc function contains information at all frequencies up to the Nyquist frequency, making it difficult to upsample accurately. Also, the peak is located at a fraction of , so even perfect upsampling by four would not catch the true peak. You can download this shifted sinc test file here.
Testing Overshoot: Sine Sweeps
Another good test for true peak meters is a sampled sine sweep at a known amplitude. The true peak of this waveform will just be the amplitude of the sine sweep, but many meters will report a higher true peak because of errors in the upsampling algorithm. Like the sinc function, the sine sweep is difficult to upsample accurately because it has information at all frequencies. We can generate a sine sweep with the following NumPy code:
You can download the sine sweep file here.
![Izotope Izotope](/uploads/1/2/6/0/126025621/909366727.jpg)
How good is the example algorithm specified by BS.1770?
Now that we have a few techniques for measuring the quality of true peak detection algorithms, let’s put these to work in evaluating the example algorithm provided by BS.1770.
The upsampling algorithm is a simple one, based on upsampling by four, interpolating with a specific kernel. For more background information on upsampling, please see this reference. The coefficients of the kernel are given in the BS.1770 specification, and looks like this:
If we save this kernel as a wave file we can use RX’s Spectrum Analyzer to visualize the frequency response of this kernel:
Here, the cutoff frequency is a quarter of the sampling rate, or 6 kHz. The ideal filter would be perfectly flat below this frequency, and then drop immediately down to dB above it. Real world resampling filters have to make tradeoffs and cannot achieve this.
As we can see, there is a fairly significant amount of ripple in the passband (below roughly 5 kHz), which may indicate that the detector will overshoot at certain frequencies. Indeed, applying this detector to our sine sweep test signal, which has a true peak level of dB, results in a measured value of dB, an error of dB.
Also, the kernel is not very steep at our cutoff frequency. This indicates that for signals with a lot of high-frequency content, such as our sinc test signal, the filter may significantly undershoot. Indeed, for our shifted sinc test file, which also has a true peak of dB, the BS.1770 detector results in a measured value of dB, an error of dB. So, even compliant meters can have fairly significant errors in their true peak detection.
Extra credit: How high can true peaks get?
We’ve now seen several signals that have true peaks higher than their sample peaks, even by more than a decibel. Is there any limit to how much higher the true peaks can be than the sample peak? This is an interesting question because if there were some limit than we would have a worst case bound of how much error any given true peak meter could have.
Unfortunately for meters, it turns out that there is actually no limit to the difference between sample peaks and true peaks.
Plan of the Proof
To show that true peaks can become arbitrarily high, we’ll explore a pathological waveform where we can make the true peak as high as we want, by adding more samples. This particular example was discovered by iZotope colleague Alex Lukin, and the rigorous proof that it had an unboundedly high true peak was found by Aaron Wishnick.
The pathological waveform we are interested in is a series of alternations between and , followed by silence. We’ll show that by adding more alternations, we can make the true peak as high as we want to.
We can start to get a feel for this waveform by manually dragging samples around in RX. Here’s what it looks like after three alternations of and :
As you can see, one true peak is already higher than the sample peak of , and it’s exactly halfway between samples. Using RX’s waveform stats window, we can see that after three alternations the true peak is dB, while the sample peak is or dB. It turns out that by adding more alternations of and , we can make the true peak even higher. Here’s what it looks like with ten alternations:
Using waveform stats, we see that the true peak is dB, while the sample peak is the same at dB.
In order to prove that we really can make the true peak as high as we want, we’ll have to dig into some of the math.
Detailed Proof
For convenience, let’s call the time of the last sample time , so that the alternations of and extend back into negative time. Also for convenience, let’s assume our sampling rate is (this will make the math a bit easier). Judging from RX, this will put the true peak at time , half way between the last and the first .
So, we need to find an equation to tell us the value of the analog waveform at time . For this, we can use the Shannon interpolation formula:
Where is our sampled signal at time , is the number of alternations and is the analog waveform at time . Since we are interested in , our equation becomes
We know from trigonometry that is positive if is even, or negative if is odd. We can express this as . So our equation becomes
Now, we plug in the fact that our signal consists of alternations between and , ending at at time 0. Note that when is even, and when is odd, since it alternates every sample. We can express this as . So, our equation simplifies to
Now, note the two terms cancel:
This is a formula for the analog level at time that only depends on the number of alternations, .
We can plot this series using Wolfram Alpha, and note that the sum diverges. We can also recognize this as a general harmonic series, which all diverge.
Knowing that the series diverges means that the more terms we add the more alternations of and , the higher the true peak will be. There is no limit to how high we can make the true peak, if we have enough alternations of and . However, since the signal is either , , or at all samples, the sample peak is always . So, knowing the sample peak doesn’t tell you much about the true peak, at least for these pathological signals.
Industry | Software industry/SIP licensing |
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Headquarters | , |
Worldwide | |
Products | audio middleware |
Website | www.izotope.com |
iZotope, Inc. is an audio technology company based in Cambridge, Massachusetts, United States. iZotope develops professional audio software for audio recording, mixing, broadcast, sound design, and mastering which can be used in wide range of Digital Audio Workstation (DAW) programs. In addition, iZotope creates and licenses audio DSP technology including noise reduction, sample rate conversion, dithering, time stretching, and audio enhancement to hardware and software companies in the consumer and pro audio industries.
Software[edit]
Product name | Release date | Description |
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Alloy 2 | August 14, 2012[1] | channel strip plugin with EQ, Transient Shaper, Dynamics, Exciter, Limiter, and De-Esser |
ANR-B | May 10, 2007[2] | iZotope's only hardware unit — adaptive realtime noise reduction for broadcast audio |
BreakTweaker | January 23, 2014[3] | drum sculpting and beat sequencing machine that blurs the line between rhythm and melody |
DDLY Dynamic Delay | February 9, 2016[4] | responds to track musical dynamics to create unique delays |
Insight | November 13, 2012[5] | CALM Act compliant essential metering suite |
Iris 2 | November 19, 2014[6] | spectral sampling re-synthesizer featuring spectral selection tools |
Nectar | November, 2010[7] | vocal production suite |
Nectar 2 | October 18, 2013[8] | |
Nectar 3 | October 16, 2018 | |
Neutron | October 5, 2016[9] | audio mixing plug-in suite including advanced analysis and metering |
Neutron 2 | October 5, 2017[10] | |
Neutron 3 | June 6, 2019[11] | |
Ozone 7 | November 3, 2015[12] | mastering suite with equalizer and dynamic eq, dynamics processing, exciter, spectral shaping processor, imager, maximizer, track referencing system and mastering assistant |
Ozone 8 | October 5, 2017[10] | |
Ozone 9 | October 3, 2019[13] | |
RX 6 | April 20, 2017[14] | audio restoration suite |
RX 7 | September 13, 2018 | |
Stutter Edit | January 13, 2011[15] | sample stutter effects and slicing |
Tonal Balance Control | October 5, 2017[10] | visual analysis tool measuring the distribution of energy across frequency spectrum, comparing audio to program-specific or custom-created targets |
Trash 2 | November 19, 2012[16] | 64-bit modeling of guitar amplifiers, distortions, delays and filters |
Vinyl | February 1, 2001[17] | record simulation and lo-fi effect |
Mobile applications[edit]
- Spire — iOS recording app
- iDrum and iDrum Mobile (acquired on December 4, 2006)[18] — virtual drum machine[19]
- Music and Speech Cleaner — audio cleanup and enhancement suite[20]
- Sonifi — mobile remix mobile application developed by Sonik Architects[21]
- The T-Pain Effect (released July 20, 2011)[22] — beat and vocal recording software with pitch correction
Third-party plugins[edit]
- Ozone Maximizer Rack Extension (released June 14, 2012)[23] for Reason — Reason 6.5 Rack Extension
- Mastering Essentials (released January 20, 2012)[24] for Acoustica Mixcraft Pro Studio 6
- Radius (released May 19, 2006)[25] — world-class time stretching and pitch shifting for Logic Pro and SoundTrack Pro
Discontinued products[edit]
- Ozone MP — analog modeled audio enhancement for Winamp and Windows Media Player
- pHATmatik PRO[26] — loop-based sampler
- PhotonShow — photo slideshow software
- PhotonTV — photo slideshow software
- Spectron (released March 6, 2003)[27] — 64-bit spectral effects processor[28]
Compatible software[edit]
iZotope's software can be used with Pro Tools, Apple's Logic Pro and GarageBand, Cakewalk SONAR, Nuendo, Digital Performer, WaveLab, Adobe Audition, Magix VEGAS, Reaper, FL Studio, Ableton Live etc.
Hardware[edit]
Izotope recently launched an iPhone-driven physical recording device competing with Zoom and Tascam, branded Spire Studio. It works wirelessly with the Spire IOS app and includes 4Gb of storage and XLR/TS ports for instrument jacks and mics in addition to the on board, internal mic. It is small, portable and not rack mounted and appears to be targeted to smaller bands and single musicians as well as home studios, as well as the podcasting and meeting sectors.
Licensing[edit]
iZotope has recently branched out its business to include software and technology licensing after ten years of developing audio processing algorithms and tools for their own software. iZotope offers development of technology for Mac and Windows platforms, Mobile, Video Game, and Embedded DSP. Clients have included Sony, Adobe, Xbox, Harmonix,[29]Smule, Sonoma Wire Works, and most recently, Blue Microphones.[30] Algorithms are delivered as a plugin or SDK for easy implementation. To date, iZotope technology has shipped in nearly 68 million products worldwide.[31]
Licensed technologies[edit]
- Mac/PC[32]
iZotope has audio technology readily available in the form of VST, DirectX, AudioUnits, RTAS or AudioSuite plug-ins. Typical uses for licensed technology for Mac or PC applications include audio finalizing, music production, audio for video, presentation audio, metering to address broadcast loudness standards, and media playback. Categories of available licensed technologies include audio enhancement, voice enhancement, audio repair tools, creative tools, DJ tools, audiophile tools, time manipulation and audio for video.
- Video Games[33]
iZotope has developed plugins for use directly in Audiokinetic WWise for audio enhancement, voice effects occlusion and room modeling. In addition, iZotope has developed sound design tools and special effects for sound designers using the FMOD middleware engine. For middleware engines supporting XAudio and Multistream formats, iZotope has a collection of licensable DSP for use in music related games or karaoke.
- Mobile SDKs[34]
- Core FX
- Audio Repair
- DJ FX
- Vocal FX
- Trash FX
- Fun FX
- Embedded[35]
Noise reduction DSP is available for use in hardware using Analog Devices SHARC and Blackfin processors. In 2012, iZotope embedded Adaptive Noise Reduction and Keyboard Click Reduction technologies on Blue Microphones' Tiki USB Mic.[36]
- Other
- Omega — realtime time and pitch control
- Radius — natural time stretching technology. Integrated into Digidesign's Pro Tools Elastic Time as well as Cakewalk SONAR. Available as a plug-in for Apple Logic Pro.
- SRC — 64-bit sample rate conversion.
Notable licensing partners[edit]
Mac and PC | Video games | Mobile |
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Artist references[edit]
Izotope Rx Sample Rate Free
- iZotope receives credit from Trent Reznor and Nine Inch Nails on the album credits of Year Zero.[37]
- American record producer Just Blaze mentions using Ozone on his latest project with Jay-Z.[38]
- Rock band from the US Garbage refers using Stutter Edit, Ozone, and Trash.[39]
- American DJ Skrillex discusses about using Ozone on his tracks.[40]
Izotope Rx Elements
Awards and accolades[edit]
- Emmy Award Technology & Engineering Emmy (2013) — RX 2[41]
References[edit]
- ^'Izotope Alloy 2'. Sound on Sound. Retrieved October 4, 2019.
- ^'Izotope ANR-B'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope Break Tweaker'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope release free DDLY Dynamic Delay'. Sound on Sound. Retrieved October 4, 2019.
- ^'Izotope Insight'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope Iris 2'. Sound on Sound. Retrieved October 4, 2019.
- ^'Izotope Nectar'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope Nectar 2'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope Neutron'. Sound on Sound. Retrieved October 4, 2019.
- ^ abc'iZotope Neutron 2 & Ozone 8'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope announces Neutron 3'. Visuals Producer. June 6, 2019. Retrieved November 21, 2019.
- ^'iZotope Ozone 7'. Sound on Sound. Retrieved October 4, 2019.
- ^'iZotope Ozone 9 Released - New AI Based Features - Exclusive Demo And Review'. Production Expert. Retrieved October 4, 2019.
- ^'iZotope RX6'. Sound on Sound. Retrieved October 4, 2019.
- ^'Izotope Stutter Edit'. Sound on Sound. Retrieved October 4, 2019.
- ^MusicTech.net (February 6, 2013). 'Trash 2 Review'. MusicTech. Retrieved October 4, 2019.
- ^'iZotope Releases Free Vinyl Plug-In'. iZotope, Inc. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^McConnon, Brian. 'IZOTOPE ACQUIRES IDRUM AND PHATMATIK PRO'. iZotope, Inc. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^'iDrum'. iZotope, Inc.
- ^'Music and Speech Cleaner'.
- ^'Sonifi iPhone App lets your fingers remix music'. Los Angeles Times. November 17, 2009.
- ^McConnon, Brian. 'T-Pain and iZotope Introduce The T-Pain Effect'. Music Marcom. Archived from the original on June 1, 2012. Retrieved July 11, 2012.
- ^McConnon, Brian. 'iZotope Releases Ozone Maximizer Rack Extension for Reason'. Music Marcom. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^McConnon, Brian. 'iZotope Introduces Mastering Essentials'. Music Marcom. Archived from the original on May 7, 2012. Retrieved July 11, 2012.
- ^McConnon, Brian. 'iZotope Releases iZotope Radius for Logic'. Music Marcom. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^McConnon, Brian. 'iZotope Acquires iDrum and pHATmatik PRO'. Music Marcom. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^'Introducing iZotope Spectron'. iZotope, Inc. Archived from the original on February 24, 2013. Retrieved July 11, 2012.
- ^'Spectron'. iZotope, Inc.
- ^McConnon, Brian. 'iZotope Technology Licensed for Inclusion in Rock Band 3'. iZotope, Inc. Retrieved July 11, 2012.
- ^'tiki FAQ'. Blue Microphones.
- ^'Powered By iZotope'. iZotope, Inc. Retrieved June 6, 2012.
- ^'Mac/Win'. iZotope. Retrieved June 6, 2012.
- ^'About iZotope | Audio Software, Plug-ins, VST'. Izotope.com. Retrieved December 16, 2017.
- ^'Audio for iOS'. iZotope. Retrieved June 6, 2012.
- ^'Embedded Audio Repair Tools'. iZotope. Retrieved June 6, 2012.
- ^'AES12: iZotope Technology Embedded Into Microphones'. Sonicstate.com. October 30, 2012. Retrieved December 16, 2017.
- ^'Year Zero'. NinWiki. Retrieved December 16, 2017.
- ^'Red Bull Music Academy'. Red Bull Music Academy. Retrieved December 16, 2017.
- ^'Archived copy'. Archived from the original on May 31, 2012. Retrieved June 6, 2012.CS1 maint: archived copy as title (link)
- ^'Archived copy'. Archived from the original on June 10, 2012. Retrieved June 6, 2012.CS1 maint: archived copy as title (link)
- ^'Winners Announced for the 65th Primetime Emmy Engineering Awards'. Retrieved February 24, 2014.
Further reading[edit]
Izotope Rx Sample Rates
- Frakes, Dan (October 7, 2008). 'Editors' Notes – An array of audio offerings at AES – iZotope iDrum Hip-Hop Edition and iDrum Club Edition:'. MacWorld. Retrieved October 28, 2008.
- Rogerson, Ben (October 6, 2008). 'iZotope Ozone 4 promises better mastering A pro sound from within your DAW?'. MusicRadar.com. Retrieved October 28, 2008.
- Alexander, Jason Scott (June 1, 2008). 'Field Test: iZotope RX Advanced Restoration SoftwareEASY-TO-USE MODULES OFFER TRANSPARENT, MUSICAL RESULTS'. Mix. Archived from the original on January 7, 2009. Retrieved October 28, 2008.
- 'IZotope Ozone 4 en janvier...'PC Music (in French). October 7, 2008. Retrieved October 28, 2008.
- 'iZotope Ozone 4 en enero de 2009'. Hispasonic (in Spanish). Retrieved October 28, 2008.
- 'RX Review in Mix Magazine - June Issue'. MixMagazine. Archived from the original on January 7, 2009. Retrieved October 28, 2008.
- 'ANR-B Review in Sound on Sound Magazine - April'. SoundOnSoundMagazine. Archived from the original on September 30, 2015. Retrieved October 28, 2008.
- 'RX featured in Electronic Musician 'Noises Off' - August'. ElectronicMusician. Archived from the original on October 20, 2008. Retrieved October 28, 2008.
- 'Ozone 3 review in Mix Magazine- Mar.2004'. MixMagazine. Retrieved October 28, 2008.
Izotope Rx Free Trial
External links[edit]
Izotope Rx Sample Rate Calculator
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