About Solid AAC the iTunes Plus Specification And Audio Recordings

About Solid AAC

Solid AAC is a Solid transcoder for creating m4a (AAC) files using the iTunes Plus specification.

Solid AAC creates an AAC audio file in two steps, first it generates a CAF (Core Audio File) rendered with an iTunes sound check profile applied to the file. If the sample rate of the source file is greater than 44.1 kHz, it’s downsampled to 44.1 kHz. Next, it uses this newly rendered CAF to render a high quality AAC audio file. Once the final AAC audio file is generated, the intermediary CAF is deleted.

But Solid AAC can do much more! You can use Solid AAC to create AAC files tailored to your needs. Some of the customizations include: Applying highpass and/or lowpass filters, applying custom samplerates, applying custom bitrates and applying custom codec quality values. Solid AAC is easy to use, drop any media to the drop location, select your settings or leave it as is to create iTunes Plus AAC files. Click Transcode and enjoy!

About AAC
AAC (Advanced Audio Coding) is a format for compressing and encoding digital audio. AAC achieves the portability and convenience of compressed and encoded digital audio while retaining audio quality that’s indistinguishable from larger digital files, such as audio from CDs.

About the iTunes Plus Specification
The iTunes Plus specification is a variable bit rate (VBR) 256 kbps AAC encoding format. iTunes AAC encoders are now able to transparently encode high definition audio, creating files that retain the small footprint, portability, and ease of use iTunes is known for.

About High Resolution Digital Recording
Digital audio, such as that on a CD, generally uses Linear Pulse Code Modulation (LPCM, often referred to simply as PCM) to represent audio signals. LPCM works by taking snapshots of the analog audio signal and assigning each a numerical value.

The resolution of an LPCM recording is determined by the sample rate (how many times per second samples are taken) and the bit depth (how many bits are used to represent each sample). Higher sample rates can capture higher frequencies, and higher bit depths can accurately represent a greater dynamic range.

The standard for CDs is 16-bit 44.1kHz resolution, meaning that the analog signal is sampled 44,100 times per second and each sample is given a value between -32,768 and 32,767. This resolution is often referred to as 44/16.

The Nyquist sampling theorem states that to accurately represent a signal one must use a sampling rate double that of the highest frequency being represented. The highest frequency audible to humans is around 20kHz; therefore a sampling rate of over 40kHz is required to accurately capture the audible range of frequencies. Compact discs’ 44.1kHz rate is adequate for this need.

Even so, many experts feel that using higher resolution PCM files during production provides better-quality audio and a superior listening experience in the end product. For this reason, 96/24 resolution is quickly becoming a standard format in the industry, and it’s also common to see higher resolution files, such as 192/24.

To view Solid AAC in the App Store click here.

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