SPX to AAC Converter

Re-encode Speex voice audio into AAC format online

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Settings

Set the AAC audio bitrate per channel. For example, stereo audio with 128 kbps set here will produce a 256 kbps file. If set to "Custom", the recommended range is ≥64 kbps.
Set the number of audio channels. This setting is most useful when downmixing channels (e.g., from 5.1 to stereo).
Set the sample rate of the audio. Music with a full spectrum (20 Hz — 20 kHz) requires values not lower than 44.1 kHz to achieve transparency. More info can be found on the wiki.

spx

Speex is an open-source audio codec purpose-built for speech compression, developed by Jean-Marc Valin under the Xiph.Org Foundation. First released in October 2002, it targets voice-over-IP, conferencing, and any scenario where spoken word needs to travel efficiently over a network. SPX files wrap Speex-encoded audio inside an Ogg container, pairing the codec's speech optimization with Ogg's streaming capabilities. Three sampling rates are supported — narrowband at 8 kHz, wideband at 16 kHz, and ultra-wideband at 32 kHz — along with variable bitrate encoding that adapts in real time to speech complexity. A standout advantage is its patent-free, BSD-licensed nature, which allowed developers to embed it freely in both commercial and open-source products. Speex also bundles acoustic echo cancellation, noise suppression, and automatic gain control, features that rival codecs typically delegate to external libraries. Although its creators officially recommend Opus as a successor since 2012, Speex remains deployed in legacy VoIP systems, archived recordings, and embedded devices where its lightweight decoder footprint is still valued.
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aac

AAC (Advanced Audio Coding) is the successor to MP3, standardized by ISO/IEC as part of the MPEG-2 and later MPEG-4 specifications. Designed collaboratively by Fraunhofer, Dolby, Sony, Nokia, and AT&T, AAC delivers superior sound quality at equivalent or lower bit rates — a 96 kbps AAC stream generally matches a 128 kbps MP3 file in perceptual quality. The codec leverages a modified discrete cosine transform combined with advanced psychoacoustic modeling and temporal noise shaping. AAC serves as the default audio format for Apple's ecosystem (iTunes, iPhone, iPad), YouTube, and many streaming services. Its first advantage is excellent compression efficiency — high-fidelity audio using significantly less storage and bandwidth. Second, the format supports sample rates from 8 kHz to 96 kHz and up to 48 channels, suiting everything from voice calls to surround sound. Third, broad industry adoption by Apple and others ensures that virtually every modern device, browser, and media player handles AAC content natively without additional plugins.
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SPX to AAC Upgrade

Move from the niche Speex codec to AAC — a modern, widely adopted format with superior compression efficiency and device support.

Privacy Protected

Your uploaded SPX files are erased right after conversion. AAC outputs are deleted from our servers within 24 hours.

Browser-Based Tool

No desktop software needed. Run your SPX to AAC conversion from any modern web browser on any operating system.

How to convert SPX to AAC

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose aac or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your aac file right afterwards

About formats

Speex is an open-source audio codec purpose-built for speech compression, developed by Jean-Marc Valin under the Xiph.Org Foundation. First released in October 2002, it targets voice-over-IP, conferencing, and any scenario where spoken word needs to travel efficiently over a network. SPX files wrap Speex-encoded audio inside an Ogg container, pairing the codec's speech optimization with Ogg's streaming capabilities. Three sampling rates are supported — narrowband at 8 kHz, wideband at 16 kHz, and ultra-wideband at 32 kHz — along with variable bitrate encoding that adapts in real time to speech complexity. A standout advantage is its patent-free, BSD-licensed nature, which allowed developers to embed it freely in both commercial and open-source products. Speex also bundles acoustic echo cancellation, noise suppression, and automatic gain control, features that rival codecs typically delegate to external libraries. Although its creators officially recommend Opus as a successor since 2012, Speex remains deployed in legacy VoIP systems, archived recordings, and embedded devices where its lightweight decoder footprint is still valued.
Initial release: October 15, 2002
AAC (Advanced Audio Coding) is the successor to MP3, standardized by ISO/IEC as part of the MPEG-2 and later MPEG-4 specifications. Designed collaboratively by Fraunhofer, Dolby, Sony, Nokia, and AT&T, AAC delivers superior sound quality at equivalent or lower bit rates — a 96 kbps AAC stream generally matches a 128 kbps MP3 file in perceptual quality. The codec leverages a modified discrete cosine transform combined with advanced psychoacoustic modeling and temporal noise shaping. AAC serves as the default audio format for Apple's ecosystem (iTunes, iPhone, iPad), YouTube, and many streaming services. Its first advantage is excellent compression efficiency — high-fidelity audio using significantly less storage and bandwidth. Second, the format supports sample rates from 8 kHz to 96 kHz and up to 48 channels, suiting everything from voice calls to surround sound. Third, broad industry adoption by Apple and others ensures that virtually every modern device, browser, and media player handles AAC content natively without additional plugins.
Initial release: 1997

Frequently Asked Questions

Why convert SPX to AAC?

AAC delivers better audio quality than Speex at comparable bitrates, and is natively supported on Apple devices, Android, and modern browsers.

Is AAC better than SPX for voice?

For general playback, yes. AAC handles a wider frequency range and enjoys universal support, unlike the speech-only Speex codec.

What opens AAC files?

iTunes, Apple Music, VLC, Windows Media Player (with codec), and virtually all smartphone default music apps play AAC natively.

Can I batch convert SPX files to AAC?

Yes — upload multiple SPX files at once and they will all be converted to AAC in parallel.

Is the conversion free?

Basic SPX to AAC conversions are free. Upgraded plans unlock priority processing and higher file size limits.

SPX to AAC Quality Rating

4.4 (16 votes)
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