The marketing material that is put forth by CSR (the creator of aptX) is pretty unclear. However, we have seen them claim that aptX delivers lossless CD audio quality sound. Given that aptX is a proprietary codec, it is not disclosed how an audio signal is compressed using this codec. Not knowing much about the nature of aptX, we were skeptical about the claims. Hence, we came up with a few simple experiments to attempt to objectively understand this codec.
Before moving on to the results, we should let you know that many of the figures will be represented in terms of spectrograms. Spectrograms are helpful to study what happens to the frequency content of a signal with respect to time. In a typical spectrogram figure, the x and y axes denote time and frequency. The magnitude of a signal at a certain time and frequency is coded in different colors: red being the largest and dark blue the smallest.
M M Signal - I Don t Know (mp3.pm).mp3
====================================================================== - TI-Vibe v0.1 for TI-89/TI-89 Titanium/TI-92+/Voyage 200 -======================================================================I. What is TI-Vibe?===================TI-Vibe is a music player for TI-68k calculators. It outputs to theI/O port what will probably be the best sound you will be able to hearon these 12Mhz devices (7 bits, mono, 22khz).II. Using TI-Vibe=================First you need to convert the audio file you want to play to a TIfile. A script is provided for an automated conversion on Windows: itis based on the MP3 encoder LAME, the sampling rate converter SSRC,and a custom Python script vibegen.py. You don't need to downloadanything except Python, everything is provided in TI-Vibe's package.* Download and install Python: * In Windows's System Properties, add the path to Python's installation directory to the PATH environment variable.* Copy the .wav or .mp3 file you want to convert to the bin/ directory of TI-Vibe's distribution. Don't choose a file too big that won't fit in the calculator's memory once converted: 22130 bytes (depending on the SAMPLE_RATE chosen, see further) are needed on the calculator per second of music. For example on TI-89 Titanium and Xpanded Voyage 200 with their 2.5MB of free archive memory, you can fill all the memory with a 117-second long song.* You may set a few parameters for the conversion. Edit vibegen.bat in the bin/ directory and change the default value of these variables at the beginning of the script: - SAMPLE_RATE: it has been configured to 22200 for a Titanium HW3. For HW1 models it should be lower, for a TI-92 Plus HW2 it should be higher. The correct value depends on the frequency of the CPU and on how fast the Flash memory chip is. You have to make a few tests to find the value which makes TI-Vibe play the file at a good tempo on your calculator. Also SSRC (the sampling rate converter) sometimes returns errors depending on the input file sampling rate (followed by Vibegen reporting "not a WAVE file"): slightly changing SAMPLE_RATE is in this case needed. - SCALE: the sound will probably be too low when played by TI-Vibe, the original file needs to be scaled. 3 is a good value, but you may write a higher one here if it is still played to low.* Open an command line console, 'cd' to the bin/ directory, and run the conversion: vibegen.bat infile[.mp3/.wav] tiname A TI group file is created ([tiname.89g], containing the wave data splitted in archived variables gathered in the folder you have chosen ('tiname'). If it isn't, a tool in the chain (scaling, mp3 decoding, sampling rate conversion, conversion to a TI file) has probably failed, read the error report for more details on at went wrong.* Send tivibe.89z and the group file to the calculator. They are TI-89 files, but may be sent to any TI-68k model. Depending on how much archive memory is left, you will perhaps not be able to send all the variables in the group file. Don't worry, TI-Vibe will still work. Caution, you may sometimes see the calculator asking for a garbage collection, just confirm, wait a few seconds, and continue the transfer.* Plug a 2.5mm to 3.5mm jack adapter into the I/O port and let the fun flood into your headphones by running: tivibe("tiname") - where 'tiname' 6is the name chosen during the conversion (the name of the folder). You can press any key to stop TI-Vibe.III. What about Linux/Mac OS/[Insert favorite OS here]?=======================================================LAME and SSRC can be built for many Operating Systems (see the linksfurther), the Python script Vibegen can be run on all the OS supportedby Python, and the batch file Vibegen.bat can easily be adapted toyour needs.IV. How does TI-Vibe work?==========================Pulse Width Modulation is used: a square wave is generated for eachsample, whose width depends on the sample's value. For a n-bit signal,we have to be able to create 2^n different types of squares, with asampling rate as high as possible. The precision achieved depends onthe frequency of the CPU and on the number of cycles required for awaiting instruction (NOP).With a 12Mhz CPU and 2-cycle long NOPs (taking into account the cyclesneeded for keyboard and input data reading), a 7-bit signal at 22khzis a good compromise (with high frequency statics due to PWM, butfortunately not too annoying).100% of CPU time is used, don't expect to be able to use this methodfor background playing in games.V. Licenses===========* Naoki Shibata's sampling rate converter SSRC ( ) and the MP3 encoder LAME ( ) are distributed under the GNU LESSER GENERAL PUBLIC LICENSE. See LGPL.txt for details.* TI-Vibe (the TI program and the scripts vibegen.bat and vibegen.py) are distributed under a BSD-like License: - TI-Vibe for TI-89/92+/V200/Titanium - Copyright (C) 2006 Olivier Armand - All rights reserved.Redistribution and use in source and binary forms, with or withoutmodification, are permitted provided that the following conditionsare met:1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THEIMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS BE LIABLEFOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIALDAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS ORSERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVERCAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THEUSE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.VI. Contacting the author=========================Ask your questions and send bug reports and suggestions to: Olivier Armand (aka ExtendeD) - Please read the whole documentation before sending any e-mail.If you find TI-Vibe useful (Er... can TI-Vibe be useful?), or if youwant to help me continue my work on TI-68k platforms, please considermaking a donation via PayPal, even a very small one, to the e-mailaddress above.VII. History============2005-04-15: v0.1 * First public release.2006-04-02: * The player and the conversion scripts works... but my Titanium is 10 times the size of my MP3 player. Mmm, perhaps I've lost again my time. Give me 13 more days to write the documentation (a good line-rate of 10 lines/day for my 12Mhz brain).2006-03-24: * First lines of code for the project.VIII. Thanks to:================* James Montelongo for sharing details on Real Sound for TI84+ for his help with TI-Vibe.* Romain Liévin and Tim Singer for the documentation on TI file formats of their TI Link Protocol Guide.* Jon Holbrook, for being an Holbrook, for his successful leak in the top right-hand corner of the Universe, and for his help in writing an indecent ReadMe file. 2ff7e9595c
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