This is done because some speakers can’t produce the low frequencies needed for the bass sounds. So taking advantage of human auditory perception, you can generate a certain pattern of higher frequency harmonics. Our brains believe we are hearing the low frequency because we “fill-in” the missing fundamental frequency. Pretty awesome!
Read more about it on Wikipedia!
Make sure not to set any “callbacks” until after Remote I/O unit is fully initialized (i.e. after calling AudioUnitInitialize)
An audio unit’s general opeartions are:
Open an audio unit (AudioComponentInstanceNew)
Configure it based on the context – AudioUnitSetProperty
Initialise the audio unit (AudioUnitInitialize)
– at this point the audio unit is in a state where it can render audio
Render audio (AudioUnitRender)
An important part of a render operation for an audio unit is to manipulate the various controls that the unit provides
to change the render effects; for instance to change the decay time of a reverb, the cut off frequency of a filter, etc.
These are called parameters, and AudioUnitGetParameter and AudioUnitSetParameter are used to interact with these.
If any reconfiguration of the audio unit is required, then:
Configure it based on the context – AudioUnitSetProperty
Initialise the audio unit (AudioUnitInitialize)
Once the host is finished with an audio unit, it closes it:
Dispose audio unit (AudioComponentInstanceDispose)
Audio units can be used programmatically (for instance a mixers could be used to render audio for a game, a generator
to play audio files, etc), or they can be hosted in Digital Audio Workstation (DAW) applications such as Logic, Garage Band.
In the DAW case, it is common for an audio unit to provide a custom view to allow the user to interact with what can be
complex DSP opearations that the audio unit performs. The view is retrieved from an audio unit through AudioUnitGetProperty
and then the host instantiates it (see <AudioUnit/AUCocoaUIView.h>)
Using RemoteIO audio unit
Decibel metering from an iPhone audio unit
Analyse Audio with RemoteIO
iPhone Core Audio tutorial
It’s hard. Jens Alfke put it thusly:
“Easy” and “CoreAudio” can’t be used in the same sentence. CoreAudio is very powerful, very complex, and under-documented. Be prepared for a steep learning curve, APIs with millions of tiny little pieces, and puzzling things out from sample code rather than reading high-level documentation.
Media is hard because you’re dealing with issues of hardware I/O, real-time, threading, performance, and a pretty dense body of theory, all at the same time. Webapps are trite by comparison.
On the iPhone, Core Audio has three levels of opt-in for playback and recording, given your needs, listed here in increasing order of complexity/difficulty:
- AVAudioPlayer – File-based playback of DRM-free audio in Apple-supported codecs. Cocoa classes, called with Obj-C. iPhone 3.0 adds
AVAudioRecorder(wasn’t sure if this was NDA, but it’s on the WWDC marketing page).
- Audio Queues – C-based API for buffered recording and playback of audio. Since you supply the samples, would work for a net radio player, and for your own formats and/or DRM/encryption schemes (decrypt in memory before handing off to the queue). Inherent latency due to the use of buffers.
- Audio Units – Low-level C-based API. Very low latency, as little as 29 milliseconds. Mixing, effects, near-direct access to input and output hardware.
Other important Core API’s not directly tied to playback and recording: Audio Session Services (for communicating your app’s audio needs to the system and defining interaction with things like background iPod player, ring/silent switch) as well as getting audio H/W metadata, Audio File Services for reading/writing files, Audio File Stream Services for dealing with audio data in a network stream, Audio Conversion Services for converting between PCM and compressed formats (and vice versa), Extended Audio File Services for combining file and conversion Services (e.g., given PCM, write out to a compressed AAC file).
- Setting a property on an audio unit requires declaring the “scope” that the property applies to. Input scope is audio coming into the AU, output is going out of the unit, and global is for properties that affect the whole unit. So, if you set the stream format property on an AU’s input scope, you’re describing what you will supply to the AU.
Make the RemoteIO unit your friend. This is the AU that talks to both input and output hardware. Its use of buses is atypical and potentially confusing. Enjoy the ASCII art:
| i o |
-- BUS 1 -- from mic --> | n REMOTE I/O u | -- BUS 1 -- to app -->
| p AUDIO t |
-- BUS 0 -- from app --> | u UNIT p | -- BUS 0 -- to speaker -->
| t u |
| t |
Ergo, the stream properties for this unit are
Bus 0 Bus 1 Input Scope: Set ASBD to indicate what you’re providing for play-out Get ASBD to inspect audio format being received from H/W Output Scope: Get ASBD to inspect audio format being sent to H/W Set ASBD to indicate what format you want your units to receive
That said, setting up the callbacks for providing samples to or getting them from a unit take global scope, as their purpose is implicit from the property names:
We received a couple requests recently for the distribution of the iPhone Operating System versions we see throughout our network. The data below represents the percentage of worldwide traffic we saw from the iPhone and iPod touch from December 14-21st.
It shows that iPod touch users lag iPhone users in upgrading their OS; 97% of our iPhone traffic comes from 3.0 or higher, compared to only 68% of iPod touch traffic.
For developers working on Android applications, platform version might become even more important than it is for iPhone given the wide variety of handsets and capabilities already available. Fortunately, the Android team has announced a device dashboard based on devices that visit the Android Market. Visit the Android developer blog for details or the actual dashbaord for the most recent data.
Note: This data is based on the number of Android devices that have accessed Android Market within a 14-day period ending on the data collection date noted below.
|Android Platform||Percent of Devices|
Data collected during two weeks ending on June 16, 2010
glPushMatrix(); // execute here your glTranslate(), glRotate(), glScale() // if you are going to change the color, then restore it manually to 1,1,1,1 glPopMatrix();
In this case, it was drawing vector art on the iPhone. We wanted to draw lines of varying widths, but iPhone does not support glPushAttrib and glPopAttrib.
Normally, if you want to change the state of a lot of different enviroment varibles, such as GL_LIGHTING, glpolygonmode, gllinewidth, things like that, you would use following code:
Below is from http://www.bradleymacomber.com/coderef/OpenGLES/ on some of differences on iPhone OpenGL
OpenGL ES Limitations (on iPhone)
The subset of OpenGL for mobile devices is missing a lot of the typical functions. The exact details may come as a surprise. The Khronos site lacks any documentation explaining this. (Presumably this is an excuse for them to sell me a book.) So I am writing down the limitations as I find ’em. Most often the convention seems to be to eliminate functionality that is a convenient re-presentation of more fundamental low-level functionality.
- No GLU library.
- Some handy functions such as
gluLookAt()will have to be replaced with manual calculations.
- No immediate-mode rendering.
- This means there are no
glEnd()functions. Instead you must use vertex arrays or vertex buffers. This is no surprise since games shouldn’t be using immediate mode anyway.
- Simplified vertex arrays.
glInterleavedArrays()function is unavailable; each array must be specified separately, although stride can still be used. There are no
glMultiDrawArrays()functions. Instead use
DrawElements(). There is also no
ArrayElement()function, which makes sense since it requires
- No quads.
- All the usual geometric primitives are supported except for
GL_POLYGON. Of course, these are provided for convenience and are almost always easily replaced by triangles.
- Smaller datatypes.
- Many functions accept only smaller datatypes such as
GL_DOUBLE. Presumably this is to save space on a device with limited memory and a screen small enough that a lack of fine detail can go unnoticed.
- This new low-level datatype is introduced to replace a variety of datatypes normally presented. For example, there is no
glColor4ub()function. Presumably this helps support devices which do not have a FPU.
- No glPushAttrib nor glPopAttrib (nor glPushClientAttrib).
- Well, this is annoying. I guess an iPhone application is supposed to be simple enough that we can keep track of all states manually, eh?
- No GL_LINE_SMOOTH.
- Enabling it has no effect.
- No display lists.
- Instead use vertex arrays or vertex buffers.
- No bitmap functions.
- Functions such as
glRasterPos*()do not exist. This means you cannot render simple bitmap fonts. Instead, textured quads must be rendered. Of course, you could always render vector fonts. Don’t let me stop you.
- Texture borders not supported.
- Probably not a big deal.
Guess that means I have to manually track some of these changes and revert them back when needed. This is not always easy to do when other parts of your program can access OpenGL without your knowledge.]]>
It was not easy to compile PHP5.3.2 on MAMP. First of all, you need to download httpd2.0.63 and PHP5.3.2. (I’m using MAMP 1.9 and Mac OSX 10.6.2)
Backup your MAMP Applicaiton first in case things go wrong.
It is in /Application/MAMP
Download software packages and save in a “source download” folder somewhere (I used ~/src/)
This step is needed to provide MAMP some build & include files from Apache httpd.
% tar jxvf httpd-2.0.63.tar.bz2 % cd httpd-2.0.63
Now you need to edit srclib/apr/include/apr.h like “#define APR_HAS_SENDFILE 0″ after run configure because get an error.
./configure \ --prefix=/tmp/httpd-2.0.63 \ --with-php \ --with-mysql \ --enable-rewrite \ --enable-speling \ --enable-ssl \ --enable-deflate \ --enable-mods-shared=all \ --with-included-apr \ --enable-so \ --enable-proxy \ --enable-proxy_connect \ --enable-proxy_ftp \ --enable-echo \ --enable-file_cache \ --enable-mem_cache \ --enable-bucketeer \ --enable-cache \ --enable-case_filter \ --enable-case_filter_in \ --enable-cgid \ --enable-charset_lite \ --enable-disk_cache \ --enable-example
The configuration settings enable the default modules that MAMP builds into their application. This will let you use the MAMP interface to turn on/off the various modules as needed (because MAMP UI controls HTTPD.CONF file).
% make % make install % cd /tmp/httpd-2.0.63 % cp -r build /Application/MAMP/Library/ % cp -r include /Application/MAMP/Library/ % cp -r modules/mod_* /Applications/MAMP/Library/modules/
% tar jxvf php-5.3.2 % cd php-5.3.2
The below configuration file uses a combination of MAMP-specific folders (/Applications/MAMP/) and Apple-provided files (/usr/).
For those that decide to use DarwinPorts to get some components, these will be located in (/opt/local/). This is a way to avoid having to go to different websites to download specific modules.
My previous MAMP version was 1.8.? and had a PHP configuration for T1LIB (–with-t1lib=/Applications/MAMP/Library). I removed T1LIB b/c not installed on MACOSX.
./configure \ --prefix=/Applications/MAMP/bin/php5.3 \ --exec-prefix=/Applications/MAMP/bin/php5.3 \ --sysconfdir=/Applications/MAMP/conf/php5.3 \ --with-config-file-path=/Applications/MAMP/conf/php5.3 \ --mandir=/usr/share/man \ --infodir=/usr/share/info \ --with-apxs2=/Applications/MAMP/Library/bin/apxs \ --enable-cli \ --with-libxml-dir=/Applications/MAMP/Library \ --with-openssl=/usr \ --with-kerberos=/usr \ --with-zlib=/usr \ --enable-bcmath \ --with-bz2=/usr \ --enable-calendar \ --with-curl=/Applications/MAMP/Library \ --enable-exif \ --enable-ftp \ --with-gd \ --with-jpeg-dir=/usr/local/libjpeg \ --with-png-dir=/usr/local/libpng \ --enable-gd-native-ttf \ --with-ldap=/usr \ --with-ldap-sasl=/usr \ --enable-mbstring=all \ --enable-mbregex \ --with-mysql=mysqlnd \ --with-mysqli=mysqlnd \ --with-pdo-mysql=mysqlnd \ --with-mysql-sock=/tmp/mysql.sock \ --with-iodbc=/usr \ --enable-shmop \ --with-snmp=/usr \ --enable-soap \ --enable-sockets \ --enable-sysvmsg \ --enable-sysvsem \ --enable-sysvshm \ --with-xmlrpc \ --with-iconv-dir=/usr \ --with-xsl=/usr \ --with-pcre-regex \ --with-imap \ --with-imap-ssl \ --with-mcrypt \ --with-mhash \ --with-freetype-dir=/usr/X11 \ --enable-zend-multibyte \ --with-gettext \ --disable-debug
NOTE: You may need to install some packages before compile PHP for some components that are not included.
You can use DarwinPorts, or download individually.
Manual method ==> http://www.teamonetickets.com/software/howto-setup-php-apache-mysql-dev-environment-on-snow-leopard.html
MacPorts method ==> http://zuzara.com/blog/2010/04/08/compiling-php5-3-2-on-mamp/
Instructions for JPEG & PNG missing files (http://www.bill.eccles.net/bills_words/2010/01/building-a-mac-os-x-server-106.html)
libjpeg, libpng, libmcrypt, IMAP c-client, libintl, gettext, libxml
Now, we need to work around a bug with inconv linking. Luckily, Apple provides a patch. Either copy the text of that patch and save it as a file or download it here.
curl -O http://www.teamonetickets.com/software/iconv.patch
patch -p1 < iconv.patch
Now that iconv will link properly, continue with our make.
% make -j3 % make install
After you have finished making PHP, it should have copied LIBPHP5.SO to your “apache” location.
libphp5.so is located where you set –prefix for apache.
It’s needed to copy to /Applications/MAMP/Library/modules.
I am not sure if this step was needed, but I also compiled a separate IMAP.SO module (which may already be build during the PHP build).
Compile IMAP first (http://www.activecollab.com/forums/topic/5844/)
cd imap-2007e/ make osx EXTRACFLAGS="-arch i386 -arch x86_64 -g -Os -pipe -no-cpp-precomp" sudo cp c-client/*.h /opt/local/include/ sudo cp c-client/*.c /opt/local/lib/ sudo cp c-client/c-client.a /opt/local/lib/libc-client.a
Reroute to MAMP directory
sudo cp c-client/*.h /opt/local/include/ sudo cp c-client/*.c /opt/local/lib/ sudo cp c-client/c-client.a /opt/local/lib/libc-client.a
An alternate method is to go into PHP source file into ext/imap/ and then you can compile just the module.
Use below to CONFIGURE custom IMAP.SO compile
./configure --with-php-config=/Applications/MAMP/bin/php5.3/bin/php-config --with-imap=/usr/local --with-kerberos --with-imap-ssl=/usr
Original IMAP-SSL problem on MAMP
You can find more information here ==> http://www.vargatron.com/2009/03/imap-ssl-with-mamp/
So instead, I just went ahead and put the PHP files on my server to test IMAP functionality instead.]]>
In summary, if we’re storing passwords, we’re probably storing those passwords incorrectly. If it isn’t obvious by now, cryptography is hard, and the odds of us getting it right on our own are basically nil. That’s why we should rely on existing frameworks, and the advice of experts like Thomas. What higher praise is there than that of praise from your sworn enemy?
- Do not invent your own “clever” password storage scheme. I know, you’re smart, and you grok this crypto stuff. But through this door lies madness– and abominations like LMHash that have ongoing, worldwide security ramifications we’re still dealing with today. Take advantage of whatever password storage tools your framework provides, as they’re likely to be a heck of a lot better tested and more battle-proven than any crazy scheme you and your team can come up with on your own. Security vulnerabilities, unlike functionality bugs in your application, run deep and silent. They can lay dormant for years.
- Never store passwords as plaintext. This feels like security 101 and is completely obvious in retrospect. But not everyone knows what you know — just ask Reddit. Store the hashes, never the actual passwords. Educate your fellow developers.
- Add a long, unique random salt to each password you store. The point of a salt (or nonce, if you prefer) is to make each password unique and long enough that brute force attacks are a waste of time. So, the user’s password, instead of being stored as the hash of “myspace1”, ends up being stored as the hash of 128 characters of random unicode string + “myspace1”. You’re now completely immune to rainbow table attack.
- Use a cryptographically secure hash. I think Thomas hates MD5 so very much it makes him seem a little crazier than he actually is. But he’s right. MD5 is vulnerable. Why pick anything remotely vulnerable, when you don’t have to? SHA-2 or Bcrypt would be a better choice.
It’s a great way to let people share their bad experiences with companies that abuse their power. In her example, thousands of people were infected with HIV from infected blood from Bayer, a pharmaceutical company. Instead of recalling the tainted product, they went ahead and sold it, figuring it would be much cheaper to get sued later. And it was cheaper. Meanwhile, the families of infected loved ones had to fight for 10+ years in lawsuits to even (1) find out there were thousands of infected people, and (2) to get any recovery. By then, their loved ones had no doubt suffered.
I’m glad Ellie came up with a great solution. It’s something I have been wanting to see, ways to use social networks and the Internet to stop all the corporate abuse. This is not about improving customer service or addressing product problems, like GetSatisfaction helps do. This gives all of us the power to highlight unethical practices of companies. Imagine how this could have addressed the isseus with Goldman Sachs, AIG, Citibank, GM, and other companies who take advantage of the average American.