The Systematic Mixing Guide.pdf
Katheleen Rullman
Author : Hamidovic Ermin
Title : The systematic mixing guide The practical handbook to make your tracks
Year : 2012
Link download : Hamidovic_Ermin_-_The_systematic_mixing_guide.zip
Foreword. Thank you for purchasing the Systematic Mixing Guide. The guide is an independent release, and as such, every sale counts. Your honesty and integrity, in light of supporting the many years of research and accumulated experience which went into authoring this text is greatly appreciated. The forerunner to this guide originally appeared in its first iteration on an online forum. It was intended to provide a quick reference to newer members of the engineering community regarding common mix processes in the pop, rock and metal genres. As its scope expanded to detail ever more (sometimes indirectly) relevant information, it became obvious that it would need to be contained within something more holistic and structured. This eBook is the final result. It should be said outright that there is no universal philosophy to mixing. The basic gist of the process is to take a set of individual tracks and make them work in concert with each other. Everything beyond that is almost entirely subjective. This book details my personal approach to mixing - a mindset that I've tried to develop and refine in a way that, at least to me, is as rational and methodical as possible. My hope is to give you a kick start on your mixing journey, and overcome some of the many hurdles I struggled with at the beginning, hopefully in a single, large bound. My firm belief is that getting the right knowledge comes from knowing to ask the right questions. This book strives to detail and elucidate upon some of the main concepts behind mixing, as well as showing practical approaches to real situations, which should serve as solid starting points for your foundation as a mix engineer. Above all, I wanted to ensure that you were provided concrete, practical information regarding most topics, rather than just arbitrary ideas and theoretical dissertations. Having said all that, this book is not one for outright newcomers to the audio realm. It assumes some degree of understanding and competency with basic audio tools and principles. If you don't feel comfortable at the very least operating tools such as DAWs, equalizers, compressors, reverbs, delays, or understand concepts such as phase, frequency and decibels, then it may be worth consolidating this knowledge before reading on. After putting down (or digitally closing, as it may be) this book, I would hope that you would be more well equipped to deal with any sessions thrown your way and know where to look down the track for further experience and knowledge as your career continues to develop. Happy reading, Ermin Hamidovic. Owner, Engineer & Producer - Systematic Productions. ...
Aims. We critically analysed the theoretical foundation and statistical reliability of the mixing-length calibration by means of standard (Teff, [Fe/H]) and global asteroseismic observables (Δν, νmax) of field stars. We also discussed the soundness of inferring a possible metallicity dependence of the mixing-length parameter from field stars.
Methods. We followed a theoretical approach based on mock datasets of artificial stars sampled from a grid of stellar models with a fixed mixing-length parameter αml. We then recovered the mixing-length parameter of the mock stars by means of SCEPtER maximum-likelihood algorithm. We finally analysed the differences between the true and recovered mixing-length values quantifying the random errors due to the observational uncertainties and the biases due to possible discrepancies in the chemical composition and input physics between artificial stars and the models adopted in the recovery.
Conclusions. We showed that the mixing-length estimates of field stars are affected by a huge spread even in an ideal case in which the stellar models used to estimate αml are exactly the same models as used to build the mock dataset. Moreover, we proved that there are many assumptions adopted in the stellar models used in the calibration that can induce spurious trend of the estimated αml with [Fe/H]. Therefore, any attempt to calibrate the mixing-length parameter by means of Teff, [Fe/H], Δν, and νmax of field stars seems to be statistically poorly reliable. As such, any claim about the possible dependence of the mixing-length on the metallicity for field stars should be considered cautiously and critically.
One of the major and long-standing weaknesses of state-of-the-art stellar models is the treatment of superadiabatic convection. A precise treatment of external convection would require 3D hydrodynamical calculations which still cannot cover the wide range of physic quantities needed to model stellar populations in our Galaxy. Moreover their results cannot be easily adopted in stellar evolutionary codes, although attempts to implement approximations directly based on 3D simulations in 1D stellar models exist in the literature (e.g. Lydon et al. 1992; Ludwig et al. 1999; Arnett et al. 2015, 2018).
An important consequence of such an approach is that neither the effective temperature nor the radius of stars with a thick outer convective envelope (i.e. late type stars) can be firmly predicted from first principles by current 1D stellar models since they strongly depend on the calibrated value of αml.
Usually this parameter is calibrated on the Sun and then the solar calibrated value is adopted for computing stellar models regardless of the mass, evolutionary stage, and chemical composition. Nevertheless, the extrapolation of the solar calibration to different evolutionary phases, metallicity, and mass ranges has been questioned both on theoretical and observational grounds. Indeed, 3D simulations of convection have suggested that the mixing-length changes as a function of stellar luminosity, gravity, and metallicity (Trampedach et al. 2014; Magic et al. 2015). Moreover, a growing amount of observations suggest that the adoption of the solar calibrated αml does not allow proper modelling of all types of stars (see e.g. Guenther & Demarque 2000; Yıldız 2007; Clausen et al. 2009; Deheuvels & Michel 2011; Bonaca et al. 2012; Mathur et al. 2012; Wu et al. 2015; Joyce & Chaboyer 2018a,b).
An alternative approach to investigate the possible dependence of αml on stellar characteristics is provided by asteroseismology. A work by Bonaca et al. (2012), based on a sample of 90 stars with precise asteroseismic and atmospheric measurements in different evolutionary phases suggested the presence of a strong dependence of αml on [Fe/H]. This analysis was recently extended by Viani et al. (2018) on a sample of about 450 stars, reaching the same conclusion that a change on αml of about 0.75 per [Fe/H] dex is needed. This value is much higher than that reported by Tayar et al. (2017), but the sample of Viani et al. (2018) contains a significant share of main sequence (MS) stars, for which the detected trend is the highest. When restricting the analysis only to the more evolved stars, Viani et al. (2018) have reported a mixing-length trend of about 0.5 per metallicity dex, which is still more than twice the value by Tayar et al. (2017).
The non-negligible discrepancies between the recent observational calibrated dependence of the mixing-length on the metallicity and the inconsistencies of these values with 3D simulations urge further investigations.
The aim of the present paper is to explore the theoretical foundation of the mixing-length calibration by means of standard and global asteroseismic observables of field stars. We followed a purely theoretical approach based on mock datasets of artificial stars, sampled from the same grid of stellar models used in the calibration procedure. The comparison between the recovered and true mixing-length values allowed us to quantify both the random errors due to the observational uncertainties and the possible biases. This kind of analysis allows us to explore the best possible scenario in which both artificial stars and stellar models are perfectly known a priori. When dealing with real stars, the reliability of the calibration procedure can only get worse.
As shown in detail in the following, even in this ideal case where the artificial stars have been computed by keeping the mixing-length value fixed to the solar value, spurious trends of the recovered αml as a function of the metallicity can be induced by wrong assumptions in the models used in the calibration, either in the chemical composition (heavy-element mixture or helium-to-metal enrichment ratio) or input physics (outer boundary conditions, radiative opacity, etc.). An example of the relevance of these effects on free parameters calibrations has been shown by Valle et al. (2017) for the estimation of the convective core overshooting parameter from binary stars.
The work is organised as follows. The estimation method and grid of adopted stellar models are presented in Sect. 2. The results from the various explored scenarios are given in Sect. 3. An analysis of the relevance of the chemical inputs assumed in the recovery is presented in Sect. 4. Section 5 addresses the possible effect of a mismatch between the recovery grid and the observations with respect to possible difference in the microscopic diffusion efficiency, boundary conditions, and effective temperature scale. Finally, some conclusions are presented in Sect. 6.
The main aim of this work is to discuss the statistical robustness of the claimed dependence of the mixing-length parameter on metallicity inferred from observations of field stars. In particular, we are interested to assess how well it is possible to recover the mixing-length value starting from standard and global asteroseismic observables, given the current errors affecting them. The nature of these errors can be statistical, owing to the achievable precision of the instrumentation, but also systematic, due to offset calibrations.
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