Audio decoder chip: compressed-format decoders that turn MP3, AAC, Ogg Vorbis or Dolby/DTS bitstreams into PCM or analog audio

01

Decoder only, decoder with its own DAC, or multichannel decoder DSP: STA013, VS1053b and CS4953xx side by side

The three parts below cover three different jobs; the output row decides what else has to go on the board.

The image above shows a QFP audio IC held in a clamshell test socket on an evaluation board with audio jacks, the arrangement used to try a decoder against real files before committing to a board layout.

The STA013 datasheet notes that its PCM interface is software-programmable to suit the DAC chosen, which is the trade a decoder-only part makes: a free choice of DAC quality, at the cost of a second chip, its clocking and its layout. [2] The VS1053b removes that second chip but fixes the analog performance at what its own DAC delivers (next section). [1]

List every format, bitrate and sample rate the product must play, the number of output channels, whether the output is analog headphone, line, I2S or S/PDIF, and the host interface available (SPI, I2C, I2S).

02

Clock and power: a 12.288 MHz crystal for 48 kHz, a 4.5× multiplier for HE-AAC v2, 76–85 mW for MP3 only, and a 500 mA core on a Dolby/DTS DSP

Decoding load varies with the format, and the datasheets show it in the clock each chip needs and the power it draws.

The STA013 datasheet gives its power two ways: the feature list says 85 mW at 2.4 V, while the power dissipation table gives 85 mW at ≤48 kHz with VDD = 3 V. Confirm the supply condition with the supplier before using the figure in a battery budget. [2]

Editorial calculation: at the recommended 3.5× multiplier, a 12.288 MHz crystal gives CLKI = 43 MHz on the VS1053b; HE-AAC v2 at 4.5× needs 55.3 MHz, the top of the CLKI range. [1] During Ogg Vorbis playback, 11 mA at the 2.6 V AVDD of the test plus 11 mA at 1.8 V CVDD is about 29 + 20 = 49 mW, before I/O current. [1] On the CS4953xx, 500 mA at 1.8 V is 0.9 W for the core and 120 mA at 3.3 V about 0.4 W for I/O, roughly 1.3 W, some fifteen times the STA013's 85 mW. [3] [2]

Give the formats with the highest decoding load (HE-AAC v2, WMA, multichannel Dolby or DTS), the crystal frequency available, the supply rails and the power budget for decoding.

03

On-chip DAC versus I2S out: the VS1053b's 18-bit DAC at 94 dB SNR, and crosstalk that drops from 80 dB to 53 dB on a 30 Ω earphone

When the decoder carries its own DAC, its analog figures become the product's audio figures. The VS1053b datasheet states them at AVDD 3.3 V with a 30 Ω load:

Editorial calculation: 2750 mVpp is about 0.97 V rms for a sine, and into a 30 Ω earphone that is about 31 mW per channel at full-scale output; with VREF at 1.23 V the 2050 mVpp output is about 0.72 V rms. [1] The datasheet gives 80 dB of channel separation with a 600 Ω load and 53 dB with a 30 Ω load, both measured through the GBUF output buffer; a product that needs more separation on headphones can take the I2S output to an external DAC and amplifier instead. [1]

Neither the STA013 nor the CS4953xx has an analog output; their analog quality is set entirely by the DAC and amplifier that follow them. [2] [3]

State the load (earphone impedance, line input), the SNR and channel separation required, and whether an external DAC is acceptable.

04

Decoder chip requirements to send

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Formats: [MP3; AAC/HE-AAC; Ogg; WMA; FLAC; Dolby; DTS]
Bitrate and sample rate: [max kbit/s; kHz]
Channels out: [stereo; 5.1; 7.1]
Output: [analog headphone; line; I2S; S/PDIF]
Host: [SPI; I2C; I2S; parallel]
Clock and supply: [crystal MHz; rails; power budget]
Temperature and package: [range; QFP, BGA, SO]

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